Invoice Button Disabled in Purchase Order Form

Dear all

Any one help me regarding the Vendor Invoice button disable in Purchase Order form.

·We create a PO & also received the goods now the PO status is Received but when I will try to generate Invoice, the Invoice button is disable & pending Invoice button is enable so I went AP>>Common>>Vendor Invoices>>pending vendor invoice>> I Deleted Pending Invoice for PO#206.

I did the following things

·Delete Pending Invoice through AP>>Common>>Vendor Invoices>>pending vendor invoice>>

·Reset usage data from tools>>usage data>>reset

·Restart Dynamics.

·Run Consistency Check & system gave the below warring/error message

“Pending or posted invoices exist for purchase order PO-206/2012.Changing the currency or the vendor is not allowed.”

Warm Regards
MS