Missing MS Windows Common Controls 6.0 reference

All,

I have the following problem. I have an excel VBA application which has been installed at my client's PCs: on 1 PC it works, while on other 2 it doesn't.

I checked what is the problem opening an unprotected version of the application - generally it crashes when running Workbook_Open macro, and the problem is clearly missing reference to MS Windows Common Controls 6.0. The client uses 32-bit Excel 2010 and 32-bit Windows 7.
EDIT: The file MSCOMCTL.OCX is physically present at the client's PC and can be browsed for manually from VBA -> Tools -> References.

I have not encountered this problem at any other PC.

Do you know how to solve it? The code has to be protected (in fact I use padlock compiler for that, but the problem seems to be independent from the compiler) and the workbook_open macro has to work smoothly, so the references cannot be edited each time manually.

Please let me know if you ever had experience with something like that? I would really appreciate help on this