HTC Desire :: Root Update Failure - Froyo Not Offering ROM

So I just rooted my HTC desire but I didn't install a new ROM. Why you may ask because all I wanted to do is install most apps to my SD card because my SD card getting full. I didn't install a ROM because I found out that froyo was not offering this and I had not updated to it but when I try to update I get a quarter of the way thought installing when the bar disappears and a yellow triangle appears behind the android.

I suspect this is because of root. I would very much like to keep with OTA updates if possible. So what would you recommend I do? Proceed with unrooting or update with a RUU or something else?
(FYI I called Talus (my carrier) and they said if the OTA update dose not work after I do a factory reset (already tried) then I could send it in for repair, so I would assume that would reset all the software on my phone thus not being rooted. Would this be an option as my phone is under warranty or would stock ROM but rooted still void it?