Midi input problems and overall midi problem.

I have Sonar X2 studio. I use sonar with notation program connected through midi with loop MIDI virtual cables for more midi ports. Everything work well if i use small ensemble, sometimes some notes are stuck. Big problems are if i have big romantic orchestra. The stuck notes are more and some part play another instrument. I dont know where is the problem, but i am 100% it is Sonar. I set up midi buffer to 10 000 (maximum) and it is better, but there are still stuck notes, but less. I try Mini Host modular beta (from Imageline) with my project, and there are not stuck notes and any other problems. I try Reaper and there are no problems too. How can i solve this problem?

I have not encountered this, so haven't needed to solve, so don't have any suggestion. All I can think of is this...a stuck note means a note-off is not being recognized. If several notes butt up right to the beginning of the next note, it's possible for notes to get stuck.
 
As an experiment, try this: select all notes, and use Process > Length to change all notes to 99% of the existing duration. See if that helps. 
 
Also, are you using the virtual MIDI loop cable with the other hosts where the project does work? Is there some way you can just export the MIDI data and bring it into Sonar so you don't have to deal with the virtual cable? Again, I have no idea if that's the problem, but it might be worth investigating.
 
Can the notation program rewire into Sonar? That's perhaps a more direct connection.