How do you debug the AppPool crashing?

I used WinDbg and i was able to extract the following error. However i do not know what's causing it? Do you guys understand these errors at all? THank you

*** ERROR: Symbol file could not be found. Defaulted to export symbols for mscorwks.dll - PDB symbol for mscorwks.dll not loaded OS Thread Id: 0x1ac4 (59) *** WARNING: Unable to verify checksum for mscorlib.ni.dll *** ERROR: Module load completed but symbols could not be loaded for mscorlib.ni.dll *** WARNING: Unable to verify checksum for System.Web.ni.dll *** ERROR: Module load completed but symbols could not be loaded for System.Web.ni.dll *** ERROR: Symbol file could not be found. Defaulted to export symbols for webengine.dll - *** ERROR: Symbol file could not be found. Defaulted to export symbols for iiscore.dll - *** ERROR: Symbol file could not be found. Defaulted to export symbols for kernel32.dll - Child-SP RetAddr Call Site 000000000879d8f0 000007f ...