There are two ways to stop this without ceasing to use iTunes or Messenger.
Either
A: Disable Messenger's +'Show song information'+ feature. This will prevent Messenger from showing your iTunes song information and thereby stop making iTunes so nervous.
Or
B: Run iTunes with administrator privileges by right-clicking the EXE, selecting Properties, Compatability, and +'Run this program as an administrator'+. This will allow you to continue showing your iTunes song information in Messenger while satisfying iTunes' histrionic need for attention; but, annoyingly, iTunes mistakes administrator privileges for a compatability mode, so it will throw a compatability alert at you every time you start it. Nod, smile, click OK, and it runs fine.