We've got a several reports about SDN5 being unresponsive, throwing Application Unavailable errors and having poor search quality in the last several days. From what it looks like, it's another windows update that became evil.

Symptoms: random "Application Unavailable" screens caused by worker pool restarts.

To diagnose the error, open the Event Viewer and look for the error below, following by a notice that asp.net was stopped unexpectedly:

EventType clr20r3, P1 aspnet_wp.exe, P2 2.0.50727.832, P3 461ef1db, P4 system.web, P5 2.0.0.0, P6 461ef1d2, P7 297c, P8 8d, P9 system.nullreferenceexception, P10 NIL.

The solution for me was to uninstall the Security Update for .NET Framework 2.0 (KB928365) and then repair the .net framework 2.0.

Unfortunately the update was pushed to fix a critical remote code execution vulnerability - so I'm not really happy with the solution, hope the new update is out soon. SDN5 runs on older Windows 2000, our newer Windows 2003 box is fine.

Found it by googling the error message, which lead me to the asp.net forum post regarding the KB928265 that also mentions that other possible issues. Internet is full of other fun ways this update breaks .net applications and reading through the reports is similar to browsing wikipedia - getting to the wet t-shirt contest page is only matter of time.

update: if you continue to see SDN fail with Application Unavailable - please let us know.