You should close all instances of Excel, then check Task Manager to ensure you don't still have any orphaned Excel sessions running in the background. If you've messed up your code development, it's quite possible such an instance is keeping the workbook open.

Until you have the code running correctly, it's advisable to use:
.Visible = True
instead of:
.Visible = False

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]