Hi, I had exactly the same problem. I solved it that way:
Go to phpMyAdmin and choose your database. Choose table wp_options. This table is not marked as crashed, but it is probably damaged! Go to operations and click “repair”. The table will be repaired.
It worked for me. After that I could insert the widgets again.
Since I’ve installed wp 2.5, tables of my database crashed about 5 or 6 times (and I installed it 5 days ago!!) I had never had this problem with wp 2.3 -.-
