The SoundTouch music server is a piece of software which would run on your home computer. It runs in the background to provide access to the music on that computer's hard drive (as part of the music library function). From this we will assume that this is a message which comes up when you try to access that music library.
For more context, can you provide some further information:
Which SoundTouch product do you own?
Do you keep your music library on a Mac or PC?
Do you use iTunes or windows media player to organize the library?
Is this error message accompanied by a 4-digit error code #?
Do other sources (internet radio, Pandora, Spotify, etc.) work correctly?
What was the Brand and model # on the new router in your home?
Does the new network incorporate multiple Wi-Fi access points for greater range?