Hi MainAdmin,

1.  Please check whether you have 4 user licenses for you and the other 3 users in QuickBooks.

2. Please keep in mind QuickBooks does not allow two users working on the tasks that both tasks are using the same file.  To give an example, when I tried to post “Bank Deposit” of 05/15,  the system will pop up the similar message that you attached.  The reason is that my assistant had the 05/15 GL opened that contained the 05/15 “undeposited fund” that I was trying the do “Make Deposit”.  Then I had to wait the other User to close that GL before I could continue my task.

Hope this help!