Water Mark picture can not be replaced by new picture

I am using crystal Report for VS2010 SP 2. [ASP.NET Project in C#]

I have implemented a Watermark with a picture say, a.jpg in the Report.

After some days, when I replaced the picture by b.jpg , the new one is not shown in report.

The new picture size is same as the old one.

I don’t know why this strange behavior is happening.

Please help.

Thanks for any help/suggestion.

Regards

Abhisek