[quote user="Jagadish Patil"]Customer : v8i 08.11.09.608
Ours : V8 08.05.02.35[/quote]
Those versions of MicroStation are very different. Some VBA interfaces in MicroStation V8i (customer version) may not be available in MicroStation 2004 Edition (your version).
[quote user="Jagadish Patil"]Windows 7[/quote]
MicroStation 2004 Edition is not certified for Windows 7. It predates Windows 7 by several years.
[quote user="Jagadish Patil"]Both using 64 mc[/quote]
Not sure what that means.
Error Reporting in Applications
You appreciate that telling us customer sees 'Error 105' doesn't really help much. That just tells us 'something went wrong'. You need some way to pinpoint the error and provide a useful message when executed on customer's computer.
I suggest that you write more comprehensive error logging into your application. That's why C# has try {} catch {} blocks.