Have you not got the latest version Seesmic yet? It's just been updated to 1.7 and now appears to be located in the Xbox Live hub instead of the usual place where applications hang out. Unfortunately, Seesmic isn't a Xbox Live title and therefore doesn't have achievements, but it's still strange how it's following suit of Shazam, which also had this issue.
Version 1.7 was supposed to address Twitter authentication issues (that's all 3rd party Twitter clients seem to do with updates) and permission alterations where users can now message authenticated accounts without actively following them. Re-authenticating your Twitter account is relatively straight forward, simply opening up the app after updating (from your Xbox hub remember?) will load the account migration wizard. This will allow you to re-authenticate your account in a few steps.
Not so long ago, our Paul Acevedo covered how Seesmic now reads out tweets to the user and this was the first step in the app taking over humanity. This is stage two, taking over Xbox Live. It's only a matter of time folks, only a matter of time!