I tried several times to install 12.1. The installer removed my old 12.0 and now the command processor won't run. I think I got tcmd to start but tcc gives and error message when I try to execute a command. I have gotten tcc to run but if I try to execute tcmd I now get the message cannot find \program files\jpsoft\tcmd12\tcmd.exe and that is the file I tried to execute.
I'll need a lot more details on exactly what you did and what error messages tcc is giving.
What version of Windows are you using? (And 32-bit or 64-bit?)
What version of TCMD did you install? (And 32-bit or 64-bit?)
What is the exact error message you get from TCC?
How are you trying to execute TCMD - from a shortcut or from the command line?
Is TCMD.EXE actually in the directory?
Have you tried doing an uninstall and then installing 12.10?