If you're using automation from Access to Excel (or I suppose between any two MS Office apps) and the application you've opened through automation won't close, it may be because of "unqualified references". For a complete explanation see http://support.microsoft.com/kb/319832.
The likely culprit is a line like:
Cells(6,3)=SomeValueVBA figures out that Cells must refer to the active worksheet of the excel application, but when it does so it leaves something hanging somewhere and bad things happen later.
Instead, specify what Cells relates to- something like:
dim xlMySheet as Excel.Worksheet ... (you have to Set xlMySheet to the worksheet in here somewhere) xlMySheet.Cells(6,3)=SomeValue
The other symptom you sometimes see caused by this error is "it works once, but then doesn't work the second time".