Missing connection

[mhw]

Why does DMD not like this? If the branch going to DLX56 is to the right of C37 it will work.

[Controls Guy]

It messes with the way they do the boolean stack.  If you move the vertical branch to the left and add another T22.Done NC contact, I think it will sufficiently untangle the stack and mean the same thing as what you have.

[mhw]

You are correct, it likes that.
Thanks!

[franji1]

This is known as "reverse power flow".  I have simplified your rung to the minimalist representation (see first attached screen shot).  Many PLCs (including DirectLOGIC and Do-more) utilize a stack for resolving contact ladder logic state (a different stack for calculating math expressions, but the principal is the same).  The PLC pushes values onto the stack, ANDs or ORs the top 2 values popping them off then pushing the result back onto the stack.  This is done multiple times within a complex rung wherever you have "sub-rungs".

The logic you have created, while fully connected from left power rail to ground right rail, cannot resolve to a simple expression of ANDs and ORs.  This strange compilation error can be seen electrically if you imagine all of the contacts in the rung as being simple switches.  So then, if only DLX55, C37, and DLX56 are CLOSED, and all the other switches are OPEN, then ELECTRICALLY speaking, DLY10 should be ON.  But you will notice that for this to be true, current must flow BACKWARDS through C37 (see the second attached picture).