I got that bug where I cannot enter buildings and menues. The weird thing here is that if I restore an older, working save and play for a while, the bug happens again. It already destroyed a lot of progress.
Here are some lines from the Debug Log:
[Log]: Contract Log: Outdated save file detected! All contracts in save file were updated!
[Log]: Flight State Captured
[Log]: Saving Achievements Tree...
(Repeats 4 times)
[Exception]: NullReferenceException: Object reference not set to an instance of an object
[Log]: Flight State Captured
(and then again Saving Achievents and again the same Exception)
I have a hunch that this is related to Kerbal Alarm Clock. The bug started to appear first when I launched a manned specraft outside of the SOI of Kerbin and wanted to set Alarms on SOI change. But I may be completely wrong.
Here is a download link. I would appriciate some pointers on how to fix this. https://dl.dropboxusercontent.com/u/3056050/persistent.sfs