Probing (move until trigger) failing occationally

[paddax]

We are using a Turbo UMAC and Macro to connect to a set of Copley drives. When performing a move until trigger the system works most of the time, however occasionally the trigger is missed and the axis continues until the target position.

 

Move until trigger command is as follows

X(M140)^0Y(M141)^0Z(M142)^0

 

I can't get any further with this problem as the entire process is controlled in the protocol between the UMAC and the Copley drives.