Can't update iPhone

[apup102]

I'm trying to update my iPhone to 4.3.3, but I keep getting this message:
"The iPhone could not be updated. This device isn't eligible for the requested build."
I have an iPhone 4, 32GB, GSM model. I have tons of space left on it. The update says that it supports iPhone 4 GSM. I don't understand. Help?

 

[GADeputy]

Try downloading the 4.3.3 firmware first and then doing a shift/Update in iTunes to upgrade it.
You can download the firmware from here: http://www.felixbruns.de/iPod/firmware/

 

[apup102]

Still didn't work.

 

[patp]

is your phone jailbroken?

 

[apup102]

No, it isn't.