It will not let me open my line-up menu.

Resolution update: At the time my issue started, i needed to edit my lineup; X-Factors and Abilities. Unable to start message came when I selected the Lineup tab. Also then received that message displayed when trying to play, rather test Solo Seasons, Battles, etc. 

Late last night, I saw a message saying my X-Factors and Abilities counts were too high. Of course, they could be as I couldn't get to my lineup. So I went to my binder and selected the last person I adjusted with abilities. I reduced the abilities to a very low level putting his card\team under the abilities level.

Making a long story short, i then successfully accessed my lineup screen. After that, I went to Solo Seasons and Battles without a problem. I'm thinking MUT erred out due to my abilities being set to high outside of the lineup screen (i.e. Binder). 

Bottom-line: if you have card(s) in your line-up, adjust them in the lineup screen, not from your binder.