If changing the app pool and then changing it back solves the problem as Asad has said, then it probably means that you (or Asad) have a .NET 1.1 app on the same machine and using the same app pool. You must not use the same application pool for 1.1 .NET apps as for 2.0 and up. Maybe the 1.1 app is rarely used but when it is used it causes the app pool to hang and therefore hangs the mojoportal app. You should put all the 1.1 .NET apps on your machine into one app pool but make a new app pool for other .NET apps 2.0 and above.
Hope it helps,