[SOLVED] Application.Calculate or F9 causing runtime / Visual Basic error

I've not found a definitive solution to this issue (which seems to appear infrequently and probably for different reasons) but here's my own particular version of this problem and my solution.

NB: to be clear, I've not actually found the solution, but I have solved the issue

'Application.Calculate' (either inline or Immediate) was causing a VBA runtime error in just this one workbook. 'Calculate' was the same result. F9 to recalculate also came up with an error. Debug found no errors, so I feared I'd corrupted an external library somehow.

I use an external module that I developed myself by Googlesifting (code pasted below) that references Microsoft Outlook 14.0 Object Library.

When I tried to F9 recalculate in Excel, it popped up with the error and then popped up the References dialog. I noticed the Outlook library was highlighted, and disabling that library fixed the issue. I've updated to the latest version of the external module and this works OK. Still not much idea what happened but it's fixed now. The main change from v3.06 to v3.07 was to remove a couple of unnecessary routines, so it seems v3.06 had a line of dodgy code that somehow caused this issue. I've not tried to isolate which line because I can't be bothered! Maybe if someone has the time to analyse the code....