you can check your relative purchase order, (RMB)right mouse bottom on the line item, find

 or directly enter the relative project ID in bellow area, depends on your real situation

Just happened to have this error recently, too.  I made Sherry’s fix above but also had to update Cost/Revenue Element per Code Part Value to show if the related GL account would be associated with Cost or Revenue.  In case this works for you, too.