Hi Amjad,
We looked at the report RDL from this perspective and we saw there was a page breaking which creates a page for every group. This particular first problematic report does not have a requirement to create different spreadsheets for each of the group. So we have fixed the RDL to not to create a page for each of the Report groups, and that seems to have fixed the issue and Excel output is coming out good.
However, there is another report which requires us to have page breaks between each of the group. Meaning that the group is setup with Group Properties->Page Breaks->Between Each instance of the Group in the RDL is checked. The report outputs about 192 groups. This report is still failing. When we export this report in Microsoft Excel it does the Sheet1 to Sheet192 in Excel. When we use the Aspose Excel its failing.
Now the options are, can you find the root cause on yourside and find a way to define a Unique name as you have mentioned in your comment based on the RDL name. OR name the sheets in the same way as that of the Microsoft Excel like Sheet1, 2 and etc.
We need this issue to be resolved soon.
Thanks,
Ragu...