Currently, an issue with the Yahoo connection causes Trillian to crash. A patch is already in the works. Until it is released, all Yahoo connections should be disabled. If that is not possible due to the crash, the file yahoo.ini in the user directory has to be edited.  It is usually located at C:\Program Files\Trillian\users\default\yahoo.ini and can be opened with the Windows Editor (not Wordpad). This file contains a line auto connect = 1, it has to be changed to auto connect = 0.