Backup Database Problem

Hello Everyone,

I am running a scheduled backup of TB twice a week and today I am getting for the first time some error messages.
I am not sure what exactly they mean and how to best deal with that.

"An error occurred while storing data of the folder \\\xxx
It is possible that the message base index file is damaged - try to delete the index file (.TBI/EBI) and re-read the folder, then try to backup again"

This happens to more than one folder but not all. 
My program resides on the C:Drive - my backup files go to an external drive.  

I am not sure where I would find the relevant TBI/EBI file?   Does deleting this index file does anything to the actual folder content?
  

-- 
Best regards,
Tom  
using TheBat! 11.0.4.1 on Win 10 , 64bit

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Current version is 9.1.18 | 'Using TBUDL' information:
http://www.silverstones.com/thebat/TBUDLInfo.html