If you happen to use PockeTwit to read and write your tweets, you should start the application and make sure check for updates is ticked with the options. Re-start if necessary.
Alternatively, head on over to here to grab version 0.82a . If you prefer, just grab the CAB to copy to your device and install from here.
Because of the changes Twitter made to their authentication and application verification system, namely OAuth being the only acceptable method, we had to wait for the writer of this (FREE!!!) program to update his code. This took a while, but TBH, the program is free, works like a dream again, and matches 98% of my tweeting needs. If it had YouTube access for video uploads (like TinyTwitter that I tried to use temporarily, but also had OAuth problems with) or possibly TwitVid, I could finally dump Qik. I just checked over at PockeTwit’s User Voice Page, and someone had already requested that enhancement. Added my vote.
Anyway, once the update is installed, start up PockeTwit, goto the Settings menu on the left, and select Accounts. Assuming it is already showing your Twitter account, click on Edit Selected, and follow the on screen instructions. One other person reported a problem with OAuth verification, it might be worth temporarily changing your phone’s default browser to Pocket Internet Explorer if this occurs. No reason I can think of that this would be the issue, but worth a shot. On an unrelated note, if you get general application errors, make sure your .NET CF is up to date. (Basically 3.5 or 3.7).
Now I just need to see how easy the program will be to operate on a device without a D-Pad, like the HTC Touch Pro 2 soon to be arriving.