MRP Recurring Req. worksheet

First off let me say i am very green to the MRP system in NAV. We have been using the MRP system for about three weeks with no problems. Today we had an error pop up when running the Recurring Req. Worksheet. Can someone provide me with a better understanding of these errors other than what is in the NAV help file on Recurring Frequency field/Recurring Method field. Why would this error be showing up now. I have been searching Customersource for detailed documentation on the MRP system, but i can not find any. Any suggestions?

Thanks

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Are you sure you have been using the “Recurring” and simply the “Requisition Worksheet” this is looking for how often it needs to recur and by what method.