When you run a webi report which is of Multi source (one is SQL server 2012/08. 2. Excel)
To fix this, opened the report in modify mode, check the tab that connected to Excel source.
Open that Tab
On left hand side - Check the Source Path (even though it shows as conencted)
Click on the ... to open the source
Repoint to that Source
Apply changes and close (you will see on right top corner drop down beside close)
Run the report, it works like charm
