Hi Ioannis,
I'm glad to hear that you have solved the issue.
Problems with Tekla BIMsight installation are:
a) If it's installed after Trimble Connect Desktop, then the plugins will be downgraded to those coming with BIMsight.
b) If BIMsight or TCD is installed (or upgraded) by multiple user accounts, that would leave multiple plugins to computer. And that would show just like Andreas's screen shot of regedit, multiple plugin versions mentioned in registry path, where should be just one version of each plugin. And following those steps that Andreas wrote, will fix the issues. But, he forgot to mention that on number 6 you should also delete all files from this folder:
C:\Program Files (x86)\Tekla\Model Sharing Foundation
It's not a big issue leaving them there, but it's nice to clear those from taking disc space.
Best regards,
Marko Myllymaa