Orders from my excel workbook to TWS, via API DDE Excel, have been working fine all day long, and in the previous weeks, but today I came across this problem: Error 28 - Out of stack space. My order got as far as the "Orders" sheet of my workbook (the line was there in the right place), and then it returned an "error 28: out of stack space" and it didn't get through to TWS - it's as if TWS didn't see it. As a consequence my 2 futures didn't get sold, even though the system thought they did. Any idea what happened?