Problem zooming in. Can only zoom in so close then get a message, minimum window.

Self learning so all is hit and miss. Initial install was ProStructures Update 1. Got an upgrade to Update 4. Working in Update 1 I could zoom in almost infinitely. When the same file created in Update 1 was opened in Update 4 the file retained this setting.

I created a new file in Update 4. In this file I can only zoom in so far than it stops and I see the message, minimum window. After spending a stupid amount of time hit and miss I managed to find the setting on a Friday, made a small change in a setting somewhere and all was working as it should. Monday morning opened the file and back to not being able to zoom in close enough. Thought I'd found the setting again but no such luck.

What setting needs to be changed to allow me to zoom in as close as I need to?