Excel 2007/Vista Business

I've had problems I've seen documented (but but resolved) elsewhere, with
Excel crashing on the execution of ActiveWorkbook.Close False. 'Cured' that
with Application.Quit (not ideal), but now, after Excel closes, the VBA
Project password input box is displayed. It takes 3 clicks on Cancel to
dismiss it. If I unprotect the VBA Project, Excel closes silently, as I
would expect.

My code is a bit complex to post here, but the ThisWorkbook module code no
longer includes Workbook_BeforeClose procedure, in case you're wondering.

Anyone come across this issue before?

TIA
Bob