What do you do when you get a "Report Application Server Failed" error - scream!

I started getting this darstedly error which provided little detail or debug info.  Well fortunately, I partitioned each piece of my report into subreports so I could isolate the subreport which was causing the issue. 

this.pageViewDetails.GetActiveDocument().GetPage(3)' threw an exception of type 'CrystalDecisions.CrystalReports.Engine.InternalException'

    base {CrystalDecisions.CrystalReports.Engine.EngineException}: {"The Report Application Server failed"}

The  subreport that was causing the issue when navigating to it contained a chart with some data grouped on a key field.  The groups also contained a field which was being summed.  So, I thought lets start deleting fields and see which one maybe causing the issue.  This took little time and it turned out to be my summary field for a group which I promptly reinserted and it started working! Doh!

Anyway,  I suspect [and don't know for sure] that upgrading my Visual Studio 2010 Crystal Reports from 13.0.0.99 to Crystal Reports 13.0.1.220 may have affected fields used on the form.

It would be great to hear from other fellow sufferers and what has caused this error to occur for them!