We have seen somewhat similar behavior. Model runs fine then one load case won't even begin to solve. One of two things usually work right off. 1) Deleting the tab and start a new study w/ entirely new set up and 2) do a "save-as" to a completely different assembly (along w/ all parts) and analyze that one.
I've also seen this type of problem when a study is a copy of a copy of a copy, etc. w/ BCs copied, added, hidden.
Oh, and when you 'save-as' don't copy the Sim files.
I don't have a simulation open at the moment but when you change the model you should right click on the study and pick UPDATE COMPONENTS. Then because body names may have changed check that all of the simulation bodies maintained their material properties.
that did it. Ctrl-Q didn't, hitting the stoplight icon didn't, but right clicking and updating did.