Things to always watch out for when troubleshooting:
- locked out users - users who have been locked out of the system because the wrong password has been entered 3 consecutive times
- out of disk space (proper monitoring would fix this problem)
- GUI display that is contrary to what is actually happening on the system. Gac'ed dll's that really aren't gac'ed. In other words, assume nothing.
- inconsistent application of permissions across environments.
- duplicate libraries/dll's on machines.
- closed ports or ports/services not listening/running. Also port conflicts. More than one service wanting to use the same port.
- services, IO connections, db connections not getting closed/terminated properly.
- logic between functions or classes that creates infinite loops