The 555 is a really nice camera. Great looks, easy to use, loads of features. HOWEVER it has a weakness where the lens fails to work.

Search this forum and you will see numerous instances. The worst part is that Pentax always claim you abused it. I had to return a 550 because the lens stopped working after the battery ran flat.
Pentax told me: "This type of problem is uncommon and would generally only occur when the camera is subject to adverse conditions." - In other words it must be MY FAULT.
Fortunately I could return the camera to Jessops as it was only 2 weeks old.

I now have the same problem with the replacement 555 that I bought.

CAVEAT EMPTOR !!

I had an Optio 550 which froze the second time I recharged the battery.

See my message to another user here: https://www.pentaxuser.com/forum/ftopic242.html

Sorry to hear you also had this problem.
It is a very annoying fault: the camera seems fine, but just won't go.

I had bought my 550 from Jessops, so simply returned it for a full refund. I also reported the issue to Pentax and can provide you with an email address if you are interested. I was assured this was not a known issue with the 555.

I suspect it's not a manufacturing fault, as it seems more like a software issue, but then you would think it would always happen.

I was reviewing a photo when the camera shut down. I wonder if low battery power-down was the cause, despite this being specifically described as a feature in the manual.

Did your battery run flat while the camera was in use?

I (registered user now) received a fair response from a Pentax representative. It is good that the company has staff to answer such queries, and that problems like those I experienced are uncommon. I feel reassured with the situation (although there were no "adverse conditions" in this case, so I'm none the wiser as to the cause).
Nonetheless, I look forward to getting an Optio 555 in the near future.

Quiddity.