Thanks Colin

Its good to know it is OK with 32 bit Excel 2010 - I had assumed the incompatibility was Excel 2007/2010; It seems it is Excel 32/64 bit

<<Correction: I incorrectly assumed Excel 2010 was 64 bit. It is 32 bit. Subsequent tests with other machines with Excel 32 bit and Windows 7 64 bit all had the same problem. Conclusion is that it appears to be a problem with Excel 2007/2010 (32 bit) compatibility>>

There is no problem when not obfuscated.

To answer your question, I have spent about 3 years on this project, so I wanted some protection. I have had to spend a few months writing code associated with hardware/software keys before obfuscating the program. I am very happy with the obfuscation. It is a serious deterrent - to attack the program would be very frustrating. The software has a small market, so I do not think it would be worth anyone's effort to attack it.

Thanks for your help