Delete the current ConfigManager user.config file located at:
C:\Users\<currentUser>\AppData\Local\Quest\{ConfigurationManager.exe_StrongName_XXXXXXXX}{ERVersion}\user.config
Please note that XXXXXXXX represents a random string, and ERVersion could be something like 3.2.2, 3.5.0.12000, etc. Kindly use the ER version where you are facing the issue.
Alternatively, you can delete all folders named ConfigurationManager.exe_strongname*.