@commander --> I am in the process of re-downloading the sdk...
I am avoiding going for the format way...it's the last resort...
Just a thought...i would like to do a checksum process on the dmg file downloaded...from where can i get the checksum of iphone sdk 2.2.1...
Thanks
amal
Also make sure to empty your /Developer folder as someone else suggested. Do this before you attempt to reinstall the SDK.
Assuming you know how to delete files/dirs from a shell, it will be much faster if you do this from terminal, rather than dragging everything to the trash and waiting for that to empty.