a part has two preferred routes and you are unable to unset one due to the fact that the option is greyed out, you will need to disable the MI_FORCE_PREF_ROUTE control flag by following these steps:
Go to Options.
Select System Maintenance.
Click on System Settings.
Open GENERAL System Settings.
Select Control File.
In the Control Item field, add MI_FORCE_PREF_ROUTE.
Go into Modify Mode and change its value from Yes to No.
Click on Exit.
After disabling this control flag, you can unset the preferred route by following the next steps:
Go to Production.
Select Manufacturing Route Maintenance.
Identify the route.
Press Unset Preferred.
However, we advise to enable the MI_FORCE_PREF_ROUTE control flag back on after correcting the routes, as it will set the preferred choice for later routes.
Alternatively, you can create a third route for that particular part and then set it to be the preferred one. This will overwrite and reset the two existing preferred routes and you will be able to select the correct one again. There is also the option of deleting one of the routes by pressing F3 in the Manufacturing Route Maintenance tab, but we advise against it if you will continue to use that particular route.