Try placing @MONTHSTART@ in quotes, i.e. '@MONTHSTART@'.
Let me know if this doesn't work.
What Sage business solution are you using?
Just to let you know that I am looking at this and will get back to you shortly.
Cool. I was going to suggest checking the format of the system variable and making sure it aligns to the column format. The other option would be to modify the column using something like a SQL CONVERT function. Not sure if this would work with Progress through.