During testing how FSB Pro trades with MT4, I received MT4-FST Library Server Error -1 reported from the expert adviser.

I was trying to connect expert with ID 110.

Since such error was reported several times from our users, I investigated the reason further.
I made a small tool that shows existing connections:

After pressing Scan button, it shows the existing connections.

I closed FSB Pro and MT4 and tried again:

We see that there are remaining connections after closing the programs. This is not normal.

I tried to remove the left connections, but without success.
I opened Task Manager and noticed two copies of MT4 running in background !!!!

I closed these copies of MT4 manually and left over named pipes was cleaned.
Now I connected successfully.

What is the lesson?
Again the problem come from MT.  When there is problem with connections, turn off FSB / FST and MT4 and clean manually remaining processes by using the Task Manager.