Application pool stopped automatically in IIS 7 -

i have 64 bit server. have changed application pool enable 32 bit dlls ("enable 32 bit dll"). after reset iis , check gives error:

error : "503 service unavailable".

i checked in iis , found application pool automatically stopped.

you typically 503 service unavailable when application pool fails 5 times in less 5 minutes. happen if credentials service account isn't correct.

try using different credentials (or use network service/local system) testing purpose. if still doesn't work, take @ event logs , share results.