This may be due to the following reasons:
Stock Requistions
The item has been progressed onto a purchase order, click 'Links' to check this, if the item is on a purchase order you will need to delete the line from the purchase order using the 'Extension' tab.
Sales Requisitions
If an item is linked to a sales order and is 'requested' you will need to delete the line off the relating sales order as you are unable to delete a requisition which is requested from a different module. If you are unable to delete the line from the sales order, please check the links to see if the line is linked to a sales invoice. If this is the case, you will need delete the line off the sales 'Outstanding' invoice, if the invoice is 'Posted' you will need to use the Maintenance Tool to revert the invoice back to 'Outstanding' (you will need to delete the invoice from Sage) in order to delete the line from the sales invoice and then the requirement. Alternatively, you will need to progress the requisition onto a non EDI purchase order and progress this through the system for a return and credit.
Similarly, if an item is requested from a different module e.g. FSM or Inter-depot Transfer you will need to trace back the requisition to this module..