I have “allow multiple copies of Toad” option checked. Running 2 Toad processes, I get a popup window every once in awhile with the following:
Cannot create file “C:\Users\roeschley\AppData\Roaming\Quest Software\Toad for Oracle\12.5 beta\User Files\CONNECTIONS.INI”. The process cannot access the file because it is being used by another process
As Mark has written to posts multiple times - running multiple instances of Toad is going to have such timing and file locking issues.
Read this thread - especially where Mark replies 
Thanks Bert.
It was a sad concession Jim made many years ago to a user who wanted to start a second copy of Toad in order to kill locked Oracle processes in the first Toad back when it was called “Kill/Trace Session.”
The nature of the product is fundamentally not one to support such an odd thing. It’s why when you have a second copy of Word open and open a document already open in another copy it simply sets focus to the first copy of Word, it doesn’t open another copy in read/write mode and synchronize every keystroke back to the first copy.
Toad is vastly more complex than Word, with dozens or hundreds of files which would have to be synchronized and contention issues surfaced to the user to make them resolve in order to pull all that off so that it made sense, and then only partial.
Even though it’s an “emergency only” option, I wish we could eliminate it, because it gives the wrong impression to some. In fact when Jim added it he put in a huge warning message which said “use this 2nd copy of Toad briefly then close it immediately when done.” But we removed that warning when we did cleanup.
Thanks for the replies. I agree, it is a bit misleading as an option with no caveat. I dont’ do this often but wanted a completely separate workspace for a set of connections to a production-like environment we are building, so as not to confuse with production but easily compare and switch between the two. I can do this by using a different version of Toad for the second connection.now that I know (or have been reminded) that running 2 of the same version is not a recommended practice.
Glad to hear you’ve got an older copy lying about.
Monitoring multiple database instances is imposible runing only one copy of Toad.