I"m receiving error " Unhandled system exception: The given key was not present in the dictionary." when trying to increase the size of Address1 field on the Frs_CompositeContract_Contact from 100 to 1000. On Employee object I am unable to edit the field.
I know is not much help, but it is something on your system as I was able to do that change without issue. Said that, the "the given key" part makes me think on the "Indexes", if you ask me I would look there to see if you have any warning:
As you can see I do have a warning, but it did not affect that change, you might have something different.