1. I uninstalled V17 - OK 2. I installed V18 for all users - OK 3. When running TC 18, it complained that is could not find ...\TCMD17\tcc.exe Cause of the problem: The COMSPEC entry in ...AppData\Local\JPSoft\TCMD.INI was not updated to the new V18 path Correction & result: Change the COMSPEC entry to the V18 path and restart TC. Everything is now OK.