Excel Custom Tab Stopped Displaying

[no_one_of_consequence]

I have a custom Excel tab that I created using a XLAM file in the AddIns folder. The custom tab has two buttons at the moment that point to two macros in the XLAM file. I recently created a new macro in the XLAM file; however, when I unzip the XLAM file to tweak the customUI.xml file by adding a new button to the custom tab the custom tab disappears completely when I zip it back up as a XLAM file. Below are details and what I've tried so far:

- I am running Excel 2007 on WinXP SP3.

- I have tried removing the new macro completely and making a slight change to the customUI.xml file to see if the change shows up. When I zip the folder back up into an XLAM file the custom tab disappears. Okay, so it's not my new macro.

- I've tried copying the file, unzipping it, re-zipping it back up (with no changes) and renaming it to the original file name, but the custom menu disappears. (I made sure that the Add On was enabled in the Excel Options.)

- When I look at the properties of the duplicated XLAM file (right click>Properties), the summary tab options are all grayed out (the original XLAM file summary tab is not grayed out).

- When I compare the file size of the original XLAM to the copy, there is a very small change in file size. This makes me think that it has something to do with the zipping process on my system, but I'm just not sure. It's one of those "right-click>Send to>Compressed Folder" things.

- As far as I can tell, nothing on my system has changed since I originally created the first XLAM file. I'm all out of ideas at this point.

Any help or ideas are much appreciated.