I have not seen any client issues from the upgrade like this but could take a look at if needed.  [email protected] 

It sounds like you may be using "SmartPosting"... Try having everybody log out of the Sage 50 company except you. Go to "Tasks" at the top of your company, select "System", and then select "Post..." (if you are able to select "Post" then this means that the entries was never posted to the ledger). Once all the data post, go to "Maintain" at the top of the company and select "Company information". Change your posting method from "Smartposting" to "Real-time" then select "OK".

NOTE: If you have more than 15 workstations in your network accessing the same company then you can keep it on "Smartposting" but if you have less I recommend that you use "Realtime" posting as this will post the data as soon as you save the transaction as noted in this client knowledgebase: SES - Sage Expert Services for Sage 50—U.S. Edition Data Services