I am testing the new (May) update on my stand-alone.  I am not able to enter a PO because I keep getting the "this vendor is not approved for this item please select another item" message.  I had the approved vendor default setting in PO defaults set to ask, but allow, and changed it to do not ask but even that did not fix it.
BTW I saved the PO that only had a second description line and the PO number advanced to next available.  At least I am not getting PO's numbered "0".

The X is in "Do not check for approved vendors".  

Cathy - you have a vendor as the primary vendor shown on the IN-A screen - but I will bet you don't have any vendors listed if you hit the Vendors button.  That vendors data is in a separate data file.  If you enter the primary vendor in the Vendors screen, it will probably work correctly.  We have seen that and we have to enter a vendor entry on the vendors screen.

Cathy,  
 
  I looked into the code and changed something that may have been causing what you were seeing. I sent it to Lynn. Ask her for a copy to see if that fixes it.  
 
BKSBVEND is the table it is looking at.
 

The latest patch (patch4) fixed this problem.  However I noticed that it broke the location pop-up in the ship to.  Before the patch, unlike others who were not seeing the location choice pop-up, I was seeing it.  Now I don't.