Backups constantly failing, consolidation not happenning

On my tasks and logs page it shows that every single backup fails and had to be re-scheduled.

here is the error

<?xml version="1.0" encoding="UTF-8" ?>

""} with GUID ''} because of error 87 (Scheduler has received a request with an invalid parameter.." module="9" time="1263809477" type="4" />

Also the consolidation doesn't work, all my backup files are still there dating back to last year, but I have it set to only keep them for 30 days.