as we've developed Boxcryptor 2.0, we decided to use .bc extension for the new version of our app and to switch to .bcc for Classic versions (1.x). This change is required mostly to have Boxcryptor for Mac working without any problems.
We also thought to make the transition less bothering to the user, so we thought it would be cool to do it automatically. But we've got some complaints about this and also our Mac version of Boxcryptor 2.0 is not yet ready, so we decided to rollback this change and maybe to come out with a better solution when Boxcryptor 2.0 for Mac is ready.
We will post this update, v.1.3.2 later today, and it's not going to be available through the auto-updates, just through direct download from our web-site.
Speaking of auto-updates, when you get a notification that a new version is available, you also can view the Release Notes, which always contains useful info about whats new/changes/etc.. I guess you skipped them this time, thats why you did not new about the renaming to .bcc.
Sorry for the delay in answering this,
just too busy working on the 2.0 for Mac and iOS :)