i feel your pain, this all looks buggy to me. I´ve been renaming the file to V4tbworkspace.rui to get rid of the point in the filename. Then closed all my workspaces and opened yours. Upon opening it, i saw these errors on the commandline:
Can not add item Insert Window to toolbar Architecture, can not be linked to itself
Can not add item Window CutOuts to toolbar Architecture, can not be linked to itself
Can not add item Update history on selected objects to toolbar History, can not be linked to itself
Can not add item New to toolbar Main_2, can not be linked to itself
The images are missing for many toolbars here too but i think there are duplicated toolbars as well, eg. with names like "Architecture", "Architecture 00", "Architecture 01". Then i´ve closed the workspace completely and created a new empty one with a new name. This created a single empty toolbar with a tab and one button inlcuded using a smiley
Then i´ve clicked on import (unter toolbar properties) and selected your tb file. It took a bit of time, gave me the same error messages and opened all toolbars as tabs. Only 2 toolbars where empty, the popup was there. I guess you´ll need to arange things further and let us know first if the duplicated toolbar names where actually there or if they have been created by Rhino during import.
The workspace file above has not to be renamed, it`s saved as rui file. @andy note the file size change after saving as rui, is this expected ? What do the errors mean ?