TeamViewer has a database of error codes. Often, when a connection fails or a license is rejected, the log files generate a long ID. A user seeing "TeamViewer 12... [Error] 0259" might concatenate that into "TeamViewer 120259."
If you cannot find a safe copy of this specific build, try these free alternatives:
What "120259" likely is
: Locate the "See previous Versions" or "TeamViewer 12" tab to start the download for your specific operating system (Windows, macOS, etc.). Choose Your Module : Full Client : For both providing and receiving support.