There are a number of issues here. First Sage 50 did not replace Simply Accounting other than a name change on a great program. 

This type of problem is a time lag between the program and the database. When the program is ready to open the database the indicators have not been turned off properly and so the program thinks it is trying to open a database that is already open. As with all good programs it does not try this operation only once and give up, after repeated tries it will stop. However, if it tries again and the situation has been resolved it will carry on and open the database. I am not a programmer with Sage but I have seen this in other programs as well. the cause is usually a combination of the program involved and all the environment in which it is running. For obvious reasons the program cannot be tested on all combinations of hardware and software in which it will be run. 

If you provide more information about the edition and version of Sage 50 which you are running and the operating system this may give the programmers a better chance to solve the problems in future releases.

I hope you do get a chance to meet the programmers. They are a great group of dedicated employees who would like to hear all of the great things you have discovered about Sage 50. Not just the complaints.

This has gone on for years. Even on a brand new computer and new Sage 50 installation. So it's not the hardware. e.g. I've been working on it for 3 days, backed up, closed and re-run with no problem. However, when I did an intermediate backup yesterday it happened for no reason. One thing about it. When this happens and I have to close the app, there are 3 ways to start up the same company again - (1) Run Sage 50, select the last company you worked on; (2) Run Sage 50, Select an existing company, and (3) double-click the SAI file. Any one of them might work when the other 2 fails. I repeat, randomly any 2 fails and one of the ways works. I've probably wasted 100 hours of my life with this Sage problem. It's pretty hard to praise the programmers.

You said..."...This type of problem is a time lag between the program and the database. When the program is ready to open the database the indicators have not been turned off properly and so the program thinks it is trying to open a database that is already open...."

So this all about the program. I'm glad you admit that it's a program flaw. The positive solution is to program it so there is no lag, it's not that hard. When there's a mistake admit it and correct it, not negatively treating it as a customer complaint.

You said..."...This type of problem is a time lag between the program and the database. When the program is ready to open the database the indicators have not been turned off properly and so the program thinks it is trying to open a database that is already open...."

So this all about the program. I'm glad you admit that it's a program flaw. The positive solution is to program it so there is no lag, it's not that hard. When there's a mistake admit it and correct it, not negatively treating it as a customer complaint.

You missed an important comment in my original reply. I am NOT a Sage programmer but I have seen this in other programs. I cannot admit it to be an error in coding the program as I have not proven my thoughts on what is causing the error. What I do stand by is the fact that the Sage programmers do an excellent job at keeping the program running year in and year out. Yes, there are problems as with all software, however, the long term track record is still pretty good in my books.

Sorry, (I apologized) if you don't agree.