Window task scheduler + Firefox Preferences error

We are running TestComplete tests on TestExecute machine using Window Task Scheduler. The browser we are using is Firefox 69.0.3. Testexecute version is 14.20. OS Window Server 2012R2

 

We have set the Task scheduler - to run the test every hour for 9 hrs.. We are getting the errors

 

You are trying to call the "Preferences" method or property of the "Sys.Browser("firefox")" object that does not exist.

You are trying to call the "setBoolPref" method or property of the "Sys.Browser("firefox").Preferences" object that does not exist.

 

No idea why it happens. We run manually the same test then no error and it work