Elaine Young 

This problem rings a bell with me... it could be related to an older version of Studio that had a similar problem.  Can you confirm what version of Studio you're using?  These are the current versions as far back as it's sensible...

Trados Studio 2022 - 17.0.5.14757
MultiTerm 2022 - 17.0.0.1685

17 - is the major version
.0 - is the service release version and will change once we have new service releases
.5 - this represents the CU number
.14757 - this is our internal build number

Trados Studio 2021 - 16.2.12.9338
MultiTerm 2021 - 16.2.1.1044

Trados Studio 2019 SR2 - 15.2.8.3007
MultiTerm 2019 - 15.0.6.56482

Trados Studio 2017 SR1 - 14.1.10018.54792
MultiTerm 2017 SR1 - 14.2.8.55461

Trados Studio 2015 SR3 - 12.3.5281.10
MultiTerm 2015 SR2 - 12.2.1657.4

The version is 2021

The version is 2021

Elaine Young 

But which one?

sorry, if there more than one version of 2021, I couldn't find more information about the version. Besides, the problem I mentioned originally was only in some projects. When starting a new project, the warn disappears.

 Elaine Young 

There are 13 versions of 2021.  I gave you a clue here: Trados Studio 2021 - 16.2.12.9338

If you look under Help -> About you'll see which version of Studio have installed.  The reason this is important is because if you have an older one it "might" be that you can update and resolve the issue.  Updates are free within the major version!  16 is your major version.