This is likely an issue with a badly set registry setting which tells the operating system which program to use to open Starteam links and where it is located. The key in question is as follows ;
The (default) key should be something like (with respect to whichever version is running, in this case 12.5 )
"C:\Program Files\Borland\StarTeam SDK 12.5\Bin\StJavaw.exe" -f "C:\Program Files\Borland\StarTeam Cross-Platform Client 12.5\StarTeamCP.stjava" -- -openurl "%1" -shared
If the path 'C:\Program Files\Borland\StarTeam Cross-Platform Client 12.5\StarTeamCP.stjava' is incorrect, or has been moved or permissions have been denied to this folder then you will see an error and you will need to ensure that the path above matches the install location of your client.