I was able to solve this issue. I had to
1) Go into the list of forms for Marketing List entity in Customization
2)De-activate the form that was modified.
3)Publish All Customizations
4)Go back into the forms list in the Marketing List entity
5) Create a new main form. This will create a duplicate form from your old one. DON’t save the form until you have fixed the customization you did prior to receiving your first error. (My issue was that I added 2 columns to the Section that was holding my members list contacts/lead/accounts subgrid.)
6) Once you fix whatever change you made. Save the form, you can name it “Test Form”.
7)Publish All Customizations
8) Go back into your list of forms for the Marketing List entity in Customization
9) De-activate your “Test Form”
10) Activate your Main Form (Managed State)
11) Publish All Customizations
Your error should go away and you should now have access to the Marketing Lists.
I hope this was helpful