Tally.ERP 9 will switch to Educational mode in case it is unable to read the TDL files. In such a scenario you have to unlink the TDL configuration pack from the respective site and create a fresh configuration pack.
To unlink the TDL Configuration pack from a site, follow the steps shown:
Login to the Control Centre using the Administrator’s Account ID and Password
In the Control Centre screen
Click Tally.NET Account or press M
In My Tally.NET Account(s) screen select the required Account ID
The Control Centre screen for the selected account id appears
Click Licensing & Configuration or press L
In Licensing & Configuration screen select the required site
In TDL Config field select Not Applicable
Accept to save
Update the license to effect the changes made