XSi humidity problems?

I have had several instances with my XSi when it is very humid when I suddenly have SD card (Sandisk Ultra II 4GB) problems. The camera will work fine for a period of time and then suddenly refuse to take pictures and display an error message that the card has not been formatted for use with the camera. At first I just bit the bullet and reformatted the card (and lost all pictures) and continued on normally. I have also been able to use PC Inspector to recover all images (very slow).

I have only noticed the problem in very humid conditions (at home in Indy after a thunderstorm and now on vacation in Florida). Is anyone else having this problem and is it dependent on the type of card I'm using or just a camera issue?

Dear Bill,

Can't help a bit on sensor cleaning, as I've never even tried it on my XTi.

But I do want to welcome another ham and new member to the POTN - you will find quite a high percentage of us here. I was raised just south of you in Columbus.

73 de Bob, W9DMK

This is probably not the camera's problem, as I've been researching about the difference between SD and SDHC cards. Technically there is no 4GB SD cards: standard SD format max. out at 2GB, anything higher needs to be in SDHC format.
It could be that the 4GB SD card itself is an overcharged version and freaks out in humid environment.