So I have been battling this problem from day 1. I disassembled all of the rails and started over. It appears that the issue may reside with my middle assembly (I purchased the kit prior to the new middle assembly so I have the old one).
I have the outer rails equal in distance end to end and diagonally. I checked several times and had a friend check as well. I tried to do the roller equal distance from the corners but am not able to achieve this.
It is when I assembled the inner rails and middle assembly (without Z axis rails installed) that I encounter issues. I can get my X axis (long axis in my case) inner rail parallel to the outer rail, but the Y axis inner to outer is not parallel. If I hold the X axis in place and try to get the Y axis parallel I can see the middle assembly physically flex. I am off about 3/8″ (axis is 32″ in length). If I get this parallel the X axis is not parallel. I have loosened up the bolts on the “Gray” pieces (same pieces as shown in assembly pictures) but it did not help.
I am not sure where I go from here.