Resolution:
Please confirm the output of BatchRegistry:

LIST REPOSITORY;

and verify that output matches the actual values of the machine that hosting Repository and the id matches the reposit.id file.

Where is your repository server being installed? Is it in the same host where you run the PCGUI?  Do you use the same TIBRV_ settings when you start up the Repository server and PC gui?

You should ensure that the client that is receiving the error recognizes the server machine via the local DNS and/or HOSTS file.  Your system admin can check this out.  Also, check the BWC_HOME/config/icrepdeamon.config file for VALID HOST = ALL and turn on the reposerver debug log (in debug mode) and possibly the repdeamon debug log if necessary and restart the repository server.

Also try updating the location in repositories with the fully qualified host name using batch registry UPDATE REPOSITORY command.
e.g.

UPDATE REPOSITORY repoid SET LOCATION host:9001;

(where repid is the one from LIST REPOSITORY;)

Why does new installation of Doc Repostitory shows the error in Pc-Gui/Designer "Repository server host is not known"?