I have the same problem with an Optio 50. Yesterday I sent an e-mail to Pentax for help.

I found out, that it can be helpfull to:
- take out batteries and put them in again
- taking some "black"-pictures in NO-LCD-mode
- finally you can "solve" problem by switching the camara some times off and on

I know, all these actions are not very practical, but at least you can take some pics...