Unable to open exported report in excel from SSRS 2008 R2

I guys,

I'm with a problem on a migration form sql server 2005 to sql server 2008 r2.

In SSRS 2005 i don't have any problem exporting my reports to excel. In the new and migrated SSRS 2008 when I try to download a report to excel, when it opens on excel it display the following message:

When I click yes, the excel sheet doesn't look like anything that I have in the report.

Does anyone know how i can fix this?

Thanks a lot,

Best of regards,

Eduardo Almeida