I have just found out that it did not post to inventoryeither.

Go into PO\main and print the daily transaction register from there

Do you have any third party modifications?  

If they did not do it the first time they have to go to the GL and do it from there.

This Transaction happened a month ago so I can not print the daily transaction register from PO/main.  I printed in PO reports the Purchase Order Recap Report and the PO prints out, the Purchase Order Receipt History Report and the PO prints out, the Purchase History Report and the PO prints out but when I print the General Ledger Posting Recap It is not on this report.  I can not print the PO from Purchase order printing, it says data is not selected for report printing but when I go into PO Inquiry I can do a quick print. I do not understand how we can receive items in and it will increase inventory count and inventory valuation but it did not post to the General Ledger.

No third party modifications

I am not sure what you mean.

You said "This Transaction happened a month ago so I can not print the daily transaction register from PO/main"  did you try and it said it was empty or are you assuming since you have done others since then it would be empty?

If it is empty then try going to GL\Main and printing the daily transaction register from there to see if it prints or if it says it is empty.

Just as a lark, select the invoice, and click the right arrow on the A/P Inquiry screen.  If it takes you to an adjustment of the same invoice, the source journal button may be on that screen.

Why it would not be in your G/L detail however, I dunno.  Especially if it was updated as you indicated.

Definitely do the Daily Transaction Register as this is a common thing where users update their transaction registers, but not the G/L - I see it ALL the time and make it a point to run the GL update every morning.