@TPICK07 Update Sunday August 27 9:30am CST USA...
As I mentioned in my first reply... The Sunday Opponent reset for MUT Solo Battles "fixed" (work around more likely) the problem of not being able to play Solo Battles.
For the second straight Saturday / Sunday, Solo Battles get stuck on the fourth game, giving the error code whenever you attempt to play that fourth game (happened at 4:30pm Saturday last week, and 3:30pm on the 26th).
When you reset opponents within the Solo Battles area (sadly losing one game for the week), Solo Battles start working again, correctly. Sunday Morning, I reset Solo Battles opponents after 9:30am, and was able to play all four Solo Battles today, the 27th of August.
Since this is the second straight Saturday bug occurs / Sunday reset works around the bug ; it should be easily isolated, doubtful if they'll ever fix it, though. They tend to do more INVESTIGATING than actual FIXING issues, these days.