Lightroom CC 2015 shutting down unexpectedly

Lr has been shutting down without reason during import quite often in the past few weeks. I often need to reopen the program, only to find that my RAW files have not been converted to DNG. Sometimes none of them.

I have worked with Lr for 10 years, and used several of its earlier versions and that has never happened before.

Would appreciate it if you could help.

Thank you.

Lis