Gris,
The first thing to chck is that the version of Word did not changed. When you develop an ActiveX control for a certain version it will only run with that specific version of Word.
You can also check the version of the DLL used in the developing maching and compair it with the une in that computer. You can check the version of the DLL by just rigth-clicking on the file and going to the properties.
I hope that helps, bet let me know if you have any questions.
Regards,
Juan Carlos
N.I.