падает apache

доброго времени суток.
есть стэк работы apache:

(gdb) bt
#0 0xb6a2280a in is_a_impl (ht=1869898083, return_value=0x8f20050, return_value_ptr=0x0, this_ptr=0x0, return_value_used=1, only_subclass=1 '\001')
at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_builtin_functions.c:657
#1 0xb6a4bc53 in zend_do_fcall_common_helper_SPEC (execute_data=0xbfc171ec)
at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:200
#2 0xb6a370e0 in execute (op_array=0x8ee8608) at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:92
#3 0xb6a4b516 in zend_do_fcall_common_helper_SPEC (execute_data=0xbfc1913c)
at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:234
#4 0xb6a370e0 in execute (op_array=0x8ee9330) at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:92
#5 0xb6a4b516 in zend_do_fcall_common_helper_SPEC (execute_data=0xbfc193fc)
at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:234
#6 0xb6a370e0 in execute (op_array=0x8ee9244) at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:92
#7 0xb6a4b516 in zend_do_fcall_common_helper_SPEC (execute_data=0xbfc19e2c)
at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:234
#8 0xb6a370e0 in execute (op_array=0x8f10798) at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:92
#9 0xb6a4b516 in zend_do_fcall_common_helper_SPEC (execute_data=0xbfc1a7cc)
at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:234
#10 0xb6a370e0 in execute (op_array=0x8f10880) at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:92
#11 0xb6a4b516 in zend_do_fcall_common_helper_SPEC (execute_data=0xbfc1aadc)
at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:234
#12 0xb6a370e0 in execute (op_array=0x8eca648) at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:92
#13 0xb6a4b516 in zend_do_fcall_common_helper_SPEC (execute_data=0xbfc1acdc)
at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:234
#14 0xb6a370e0 in execute (op_array=0x8eca5a4) at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:92
#15 0xb6a4b516 in zend_do_fcall_common_helper_SPEC (execute_data=0xbfc1b07c)
at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:234
#16 0xb6a370e0 in execute (op_array=0x8eca500) at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:92
#17 0xb6a4b516 in zend_do_fcall_common_helper_SPEC (execute_data=0xbfc1b2fc)
at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:234
#18 0xb6a370e0 in execute (op_array=0x8e61738) at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:92
#19 0xb6a4b516 in zend_do_fcall_common_helper_SPEC (execute_data=0xbfc1b6bc)
at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:234
#20 0xb6a370e0 in execute (op_array=0x8e60f80) at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:92
#21 0xb6a4b516 in zend_do_fcall_common_helper_SPEC (execute_data=0xbfc1ba4c)
at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:234
#22 0xb6a370e0 in execute (op_array=0x8e5baac) at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:92
#23 0xb6a4b516 in zend_do_fcall_common_helper_SPEC (execute_data=0xbfc1bfac)
at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:234
#24 0xb6a370e0 in execute (op_array=0x8e3d8e4) at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:92
#25 0xb6a4b516 in zend_do_fcall_common_helper_SPEC (execute_data=0xbfc1c3ac)
at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:234
#26 0xb6a370e0 in execute (op_array=0x8e3f810) at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:92
#27 0xb6a4b516 in zend_do_fcall_common_helper_SPEC (execute_data=0xbfc1cbbc)
at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:234
#28 0xb6a370e0 in execute (op_array=0x8cca890) at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:92
#29 0xb6a4b516 in zend_do_fcall_common_helper_SPEC (execute_data=0xbfc1da9c)
at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:234
#30 0xb6a370e0 in execute (op_array=0x8cbd900) at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:92
#31 0xb6a4b516 in zend_do_fcall_common_helper_SPEC (execute_data=0xbfc1ddac)
at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:234
#32 0xb6a370e0 in execute (op_array=0x8c27d70) at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:92
#33 0xb6a4b516 in zend_do_fcall_common_helper_SPEC (execute_data=0xbfc1df4c)
at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:234
#34 0xb6a370e0 in execute (op_array=0x8c0b970) at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:92
#35 0xb6a4b516 in zend_do_fcall_common_helper_SPEC (execute_data=0xbfc1e36c)
at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:234
#36 0xb6a370e0 in execute (op_array=0x8c09948) at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend_vm_execute.h:92
#37 0xb6a11820 in zend_execute_scripts (type=8, retval=0x0, file_count=3)
at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/Zend/zend.c:1215
#38 0xb69c7743 in php_execute_script (primary_file=0xbfc20628) at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/main/main.c:2028
#39 0xb6a89910 in php_handler (r=0x8c4c658) at /build/buildd-php5_5.2.6.dfsg.1-1+lenny13-i386-rXrYSv/php5-5.2.6.dfsg.1/sapi/apache2handler/sapi_apache2.c:648
#40 0x0807a239 in ap_run_handler ()
#41 0x0807d651 in ap_invoke_handler ()
#42 0x0808af30 in ap_internal_redirect ()
#43 0xb65fb6c3 in ?? () from /usr/lib/apache2/modules/mod_rewrite.so
---Type <return> to continue, or q <return> to quit---
#44 0x08c4c648 in ?? ()
#45 0x08c42310 in ?? ()
#46 0x00000000 in ?? ()

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какая строка является причинной? куда дальше копать?