What were you trying to do at the time?
If it was when opening a file, then read on:
I used to get this a lot when running SSMS via "Run As Administrator" on Windows 7, trying to open files that reside on mapped drives. (When running SSMS as administrator you cannot simply drag a file from Windows Explorer to SSMS).
By accident I found this work-round:
File > Open > File
In the dialog that opens, in my case all mapped drives are initially marked with a red cross
Select the big button "My Computer" on the left
Right-click the mapped drive you want > Open
(Windows Explorer opens - wait a few seconds and then close Explorer)
Right-click the drive again > Select
In my case I can now navigate to the file I need without crashing SSMS
As a bonus, the next time you do File > Open the drives are no longer marked with a red cross - no idea why.
Best of luck ...