Hello Graeme Lorimer ,

***EDITED***

Our support team have now the proper correct solution for this-

1. Go to C:\ProgramData\SafeNet Sentinel\Sentinel RMS Development Kit and rename the System folder
2. Open CMD (with admin rights) enter the following command : cd C:\ProgramData\Package Cache\SDL\SDLTradosStudio2021SR1
3. (updated version in CMD) lsinit.exe –debug
4. Run Studio installer

(To open CMD -

Press Windows+R to open “Run” box. Type “cmd” and then click “OK” to open a regular Command Prompt. Type “cmd” and then press Ctrl+Shift+Enter to open an administrator Command Prompt.

Thanks, I checked the article and seems long and complex. Considering there are several people experiencing the same problem and error message, I expect the Studio people to look into and give an answer to the problem now. 

Graeme Lorimer

The Studio people have looked into it and this is the solution.  Please try the steps Steve outlined above.  It's quite straight forward and only takes a minute.

Well Paul, as you can see Steve edited his comment. That WAS NOT the comment I was answering, but the previous one which was not simple and straight forward. I'll try this one. Have  a nice day

Actually it is not at all straightforward... it says "rename the System folder" but doesn't say what to... 
For most people "open CMD" is not a meaningful instuction... 
I don't understand step 3 AT ALL, even though I'm not entirely stupid, I hope. 

OK, so this is the clearer form of the above instructions (for me, maybe it is helpful for others too):

1. Go to C:\ProgramData\SafeNet Sentinel\Sentinel RMS Development Kit and rename the System folder to anything you wish
2. Open CMD (with admin rights) enter the following command : cd C:\ProgramData\Package Cache\SDL\SDLTradosStudio2021SR1
3. Still in CMD, type the following text: lsinit.exe –debug
4. If the system prompts you, allow the Isinit.exe file to make changes on the system
5. Run Studio installer

And thank you for the instructions, but this is WAY to difficult a solution for a general error. The installer should be changed or the problem should be solved in some other, more user-friendly way. As an alternative, these instructions should be provided with the installer in as many languages as possible...