Parameter linking - could not add entry for "rateAC"

[Samuel Bloomfield]

I recently updated to BEAST v2.7.3 and wanted to link some of the site models after running bModelTest. In BEAUti I chose the GTR substitution model, but when I clicked "Allow parameter linkage" I got an error for each base substitution similar to the following: "could not add entry for rateAC". I have set up multiple XML files in BEAUti before just like this, but this has never happened before. Has anyone had this error come up before and found a fix, or should I just revert to an earlier version of BEAST2?

Thanks,
Samuel