The two obvious factors that can cause a Set Field step to fail: Incorrect Syntax and Incorrect Table Occurrence Context are not the issue here. You are using correct syntax and you are on the correct layout at the time the steps execute.
How do you know that the variables have the correct value?
If you are watching them in Advanced's data viewer, are any error codes appearing at the bottom of the script debugger? Do you see any other scripts, performed via script trigger, popping up in the script debugger?
Are there any auto-enter calculations defined for the target fields?
NO errors come up I have attached a screan shot of the whole lot. the red bit is where the error occures in the yellow bit you can see it worked
The red bit may never execute depending on how your Else IF Evaluates.
From your first post, the yellow flagged step was one that you originally said didn't work....
Sorry my mistake the yellow bit works. The bit that fails is part of the scrip that ignores the calculated amount if it falls bellow the minimum threshold (a retainer) or ignores the calculated amount if the have a set monthly fee which is entered into the "minimum_Charge" field.
there is another option where clients vary the amount on a month by month basis and this bit works, but it dosn't use a set field function.
Found it I had an extra o in the word amount when I set the variable