I have a couple of files created on Win7 with Excel 2007 (12.0.6545.5000). One is just over 1 Mb in size, the other is 637k. They are both .xlsm files. They both contain rather extensive VBA code. They are one-way linked via VLOOKUP. They both contain a fair bit of formatting, conditional formatting, and calculations but nothing that I would consider extraordinary.

Knowing that I would be sharing these files (as read-only) with users on multiple operating systems and versions of Excel, I went so far as to write a build-a-release routine for each that strips out the VLOOKUP() functions (writing the looked-up data directly to the cells) and other now unnecessary calculated fields, strips out the buttons (that invoke macros), and saves each file in .xlsx format (presumably stripping out the macros).

This has all been working fine for weeks. Today users on Mac 2008 (12.2.6) receive the message "the file might have been damaged or modified from its original format" when they try to open.

Things I have tried:
- Open & Repair, then start over
- Save as .xls format
- Save as .xlsb, then start over
- Manually perform the steps to save a "release" version (remove buttons, remove unnecessary calculations, save as .xlsx)

One other interesting note: Since I do not personally have a Mac here at the office, I tried opening the files in OpenOffice 3.1. No matter what format is used (.xlsx, .xls), OO reports that I am trying to open a file that contains macros. Apparently, Save As does not actually strip the VBA code from the file. I'm wondering if there is a way to RELIABLY and ACTUALLY strip the code out.

Nothing is making a difference. Suggestions?