The default thread stack for Apache binary is 256Kb [1] However, apr_thread_create() allows to use a different stack size (apr_threadattr_stacksize_set). The value used is stored in the global variable ap_thread_stacksize which can be set in ThreadStackSize at httpd.conf http://httpd.apache.org/docs/2.2/mod/mpm_common.html#threadstacksize
Can you confirm that increasing it fixes your problem?
It surprises me that Pierre recommended tweaking the PE header instead of the config option.
[1] Here are the relevant fields for httpd-2.2.17-win32-x86-openssl-0.9.8o.msi 40000 size of stack reserve 1000 size of stack commit 100000 size of heap reserve 1000 size of heap commit