In Dec 2019 a number of practices started receiving "Index Does Not Exist" error messages, or experienced various other side effects stemming from the same problem.
This was caused by Windows Defender (and possibly other Anti-Virus products) detecting a false positive in the contents of various Medilink data files, specifically index files such as !DUPLCTE.PX.
The detected item may be listed as: Win32/Generic.NW!ml
However these files are not harmful in any way, they are simply database files to help the program find things more quickly.
The Anti-Virus removing these doesn't seem to damage the data itself, but it does mean that the index needs to be recreated. The program relies on these indices and won't work properly without them (it may not always show the error message, and instead just behave erratically).
To repair the missing indices:
1. Get everyone out of Medilink.
2. Run the Service Backup tool.
3. Try and recover files via Anti-Virus quarantine area.
4. Copy all files from TUTORIAL and paste it in to DATA but skip the existing files (be very careful not to overwrite!).
5. Run Table Rebuild tool.
To ensure this problem does not re-occur you must configure Anti-Virus products to exclude the Medilink folders on all PCs (i.e. the local C:\MEDILINK32BNT folder and your server folder e.g. \\SERVER\MEDILINK).