Yes, the "XXX" part in the debug log is the task position value. But at that point it is already parsed and converted to integer so if you actually see the value in the log then the conversion is not causing the problem. I can try to take a look at the issue if you send the Rainlendar's debug log
to me (use the support email address and include a link to this forum thread). If you have multiple calendars enabled please disable all the others so that the log will contain only the calendar which has the problem.