Dear friend!
1. After you use R19, click stopweblct and run the name of the end process. Then run R21.

2. Check the user manuals of the two versions to find out whether their running environment is different from the current environment. If yes, configure the environment as required in the manual before running the LCT.
3. It is not recommended that you install multiple LCTs on the same PC. This may cause incorrect records in the system database.
You can also read this web page:
How Do I Switch Among Different Web LCT Versions?
Thank you!