InvalidSetError?

I am at a loss as to how to interpret this error. I'll try and lay this out as simply as possible.

I am working on a paperwork package for the selling of multiple vehicles. Some line items are divided evenly amongst the number of vehicles sold. If it is not possible to divide the item evenly, I have written a document-level function which calculates the offset in cents:

function remainderCatch(TotalField,PerField)
{
var PerRounded = round(PerField,2);
var Count = this.getField("SOLD_COUNT").value;
var Offset = PerRounded * Count;
var RemainderRaw = Offset - TotalField;
if (RemainderRaw == 0) {
   event.value = PerRounded
} else {
   event.value = (TotalField - ((Count-1) * PerField))
}
}

FYI:  The "round" function is a separate document-level function which rounds to the nearest decimal place of your choosing, the hundredths place in this example).

I have 5 fields which call this function, all under Vehicle #1 (so that only the first vehicle's numbers are adjusted). For this example, the line item I'm working with is called "DEPOSIT.0" (customer down-payment).

Calculation script under "DEPOSIT.0":

var DepositTotal = this.getField("TOTAL_DEPOSIT").value;
var DepositPer = this.getField("DEPOSIT_PER").value;
var Count = this.getField("SOLD_COUNT").value;
if (Count > 0)
event.value = remainderCatch(DepositTotal,DepositPer);
else event.value = ""

The calculation works just fine and I am seeing the correct numbers when it is executed. However, I am getting error messages in the console for each of the 5 fields which call this function, and all of them look like this:

InvalidSetError: Set not possible, invalid or unknown.
Event.value:7:Field DEPOSIT.0:Calculate

Can anyone see anything wrong with either code? I cannot figure this out.

Thank you so much in advance!