SQL Server - Report using excel sheet as data source not working when deployed to production.

I have a set of SSRS reports that use an excel sheet as a datasource.
Now when I preview the reports or run them in the Visual Studio IDE on my local machine i.e
the development machine, the reports run fine & display all correct results.

However, when we deploy the reports to the Production machine which is on a separate server,
the following error message is displayed :
"The current action cannot be completed. The user data source credentials do not meet the requirements to run this report. Either the user data source credentials are not stored in the report server database, or the user data source is configured not to require credentials but the unattended execution account is not specified. (rsInvalidDataSourceCredentialSetting)"

I've copy pasted the connection string used for connecting to the excel file as reference :

Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\MyFolder\CurrentRRFile.xlsx;Extended Properties="Excel 12.0;HDR=Yes;";

The excel file has also been uploaded to the machine housing the reporting server (i.e to C:\MyFolder location)

The most likely scenario is that the windows account your IIS app pool runs under doesn't have permissions to the folder and/or the file in it.  Go right click on the folder in Windows Explorer and grant the appropriate permissions.  The windows account in question is probably Network Service.