Thanks for the tip enigmatic. I gave your solution a try but it didnt work for me. Im crashing later on in the process.
Just a S.W.A.G. (scientific wild assed guess) but it kinda sounds like you might not have read/write/alter permissions on the sessions directory?
I never got quite as far as ID’ing specific modx code that was crashing the debugger.
As of a few days ago, I fired up a trial of Zend studio 7.1 and attached it’s debugger to some modx processes --- but that was also crashing fastcgi too. So that’s two, out of two, debuggers down.

Only a few more to go...
For me on IIS x64, running everything only in 32 bit mode (IIS, fastcgi, php), then trying all combinations of vc9 or vc6 builds and php versions 5.2.11, 5.2.13, 5.3.1, or 5.3.2, without exception, all crash fastcgi with the same error.
Doesnt matter if im using nusphere phped debugger (correct dbg.dll versions with each php vers, of course) or the zend debugger -- they all exit with a M.S. Global error msg of
AppName: php-cgi.exe AppVer: 5.2.10.10 ModName: php_pdo_mysql.dll ModVer: 5.2.10.10 Offset: 00002580 (appver: & modver: values vary depending on php version, of course)
and the same page returned error msg for all versions of:
<terminated, exit value: -1073741819>
Im currently scouring through all the php bugs where the pdo/mysql dll leaves mysql connections open and crashes the cgi. I was hoping to NOT have to debug these debuggers, but it looks like that’s what im in for. {sigh

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