Map Series problem with pageRow

[MarkBinder]

I'm using a map series in my ArcGIS Pro project to create a series of pdf maps. I have a Python script to create the pdf maps.

When I try to use pageRow to get the name of the map from the index layer I keep getting an error: ValueError: Type names and field names must be valid identifiers: 'SWS_Pages.OBJECTID'. 

My script worked just fine on a different project; the only difference I can see is that on this current project my index layer has a join so the field names have a period between them. Does pageRow see the period as an invalid character and then throw an error? 

Is there another way to do this? I tried using the getattr() function but with the same result. 

Thanks.

[DanPatterson_Retired]

and making the join permanent isn't an option? 

The "." in the field name isn't a real name, but identifying the fact that the dot.notated fields belong to the joined table

[MarkBinder]

I have the join so that I can make one change in the table and it changes the features in the index layer without having to go feature by feature and change things.