This issue has been caused due to the loss of connection details, to resolve this issue please do the following:
Click Options
Click System Maintenance
Click System Settings
Click General System Settings
Click Control File
Press F5 in the 'Control Item' field and search for 'SSRS_2010' and click on Select for this control flag, then press Enter
Enter modify mode by pressing Ctrl + M
Click on the drop down arrow in the 'Value' field and set this to 'Yes', click Exit
Click Options
Click System Maintenance
Click Data Manager
Click Database Maintenance
Click SSRS Web Service URL
Here you will need to enter your SSRS Web Server address which will look similar to this 'http://servername:54321/ReportsServer'. You will only need to enter your server name.
Click OK
