1) Disable custom error document for 500 error.

You can do it directly through Plesk Control Panel.

Plesk CP > domains > domain name > Web directories > Error Documents tab > Find Error 500 > Click on it > Select type `Default`.

2) Try removing the folowing lines from your global.asa (it's sometimes automatically put in):

PROGID="MSWC.MyInfo">


Enjoy...

-- Swapnil Mankar