Argument Not optional - But no reason

Hello
I have a subform and when you double click on any field it remembers 3 fields from the record you are in and stores them. I have 3 fields called [section], [losthrs], [stdhrs]. It works perfectly and stores the data from [losthrs] and [stdhrs] fields, but throws up "Argument not optional" for the [section] field.... Can not see a reason why, it is just a simple text field...

I have even tried 'pausing the code' and using the immediate window to show the field values, again losthrs and stdhrs are fine, section gives "Argument not optional"

Am i missing something, i am going mad because it make no sense to me....

thanks

Argument Not optional - But no reason