Question:
While using multiuser mode below error pops up and we could not save the model.
Error - Unable to save. Try 'save as' instead...
 
 

Answer:

To fix this, close Tekla Structures on all connected devices.  Next, restart multiuser server machine and try opening the same model again in multiuser mode. The users should now be able to save the model.

The error states that somebody has opened the same model using different multiuser server machine within the same network. This means that there are multiple machines on which multiuser server is installed. However, you should use only one multiuser server machine for all models and users within one organization.