I found this link, http://www.nwds-ak.com/WebResources/D... and tried many many many paths after Data Source....why why why it doesn't happen anything?

Here's the error report:
There was an error while executing the configured data source: An error occurred while executing the data source (Code: -2147467259): 'e:\wwwroot\Portals\0\test1.xls' is not a valid path. Make sure that the path name is spelled correctly and that you are connected to the server on which the file resides.

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Just want to add that on my localhost personal pc, with the same file (test1.xls), this connection strings works perfectly:

Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\test1.xls;Extended Properties="Excel 8.0;HDR=Yes;IMEX=1"

I really don't know how to point out the path (Data Source) for internet (server) file for DNN installation.

A late reaction, but, people with excel file connection strings will end up at this post. So, this is not just for you Dimitar.

In DNN6+Reports, the connection string to a Office 2007 file looks quite similar.
Provider=Microsoft.ACE.OLEDB.12.0;Data Source=c:\myFolder\myExcel2007file.xlsx;Extended Properties="Excel 12.0 Xml;HDR=YES"; (from http://www.connectionstrings.com/excel-2007)

The path to the data source must be an absolute path.
Then to make things work you must have a SQL query in the Query box. That query selects from a database area you created in your excel file "Select * From ProjectOverview;".

I hope this helps somebody.