Couple questions for you:

- Is the guitar an official device or is third-party?

- Do the LED lights blink when you try to connect?

- Did you try replacing your batteries?

I would recommend clearing the SYNC memory and try to sync the guitar again. To clear the SYNC memory:

Turn the on Wii console. When you see the Health and Safety screen, open the small flap on the front of the Wii console to find a red button labeled "SYNC."

Press and hold the SYNC Button down for 15 seconds. This will clear all the syncs on the Wii.

With the first Wii Remote you wish to sync, remove the battery cover on the back of the Wii Remote to find a small red button just below the batteries.

Press and release the small red button just below the batteries on the Wii Remote; the blue lights on the front of the Wii Remote will blink.

Quickly press and release the red SYNC button on the inside of the white flap on the front of the Wii console.

When the Player LED blinking stops and stays lit, the syncing is complete. The LED that is illuminated indicates the player number (1 through 4).

This sync procedure must be followed for each additional Wii Remote added to the system.

Did you try re-syncing them, the way you're supposed to when you first purchase the device? It seems like this issue is pretty common.

Have you tried contacting the developers directly? Since this is a common problem amongst consumers, they likely have information and CSR's prepared for handling this issue. Let me know if you need further direction.