Problems looping a XP-100

[loki]

Hi guys, some time ago i built a loop box to put some effects in it and exclude them from the signal chain whenever i wanted to... it works perfectly, but if i try to put the Digitech XP-100 in the loop, when i stomp on the switch everything goes mute. seems like the chain loop send ---> XP-100 input ---> XP-100 effect out ---> loop return doesnt provide a suitable loop... i've also tried using the dry output but got the same results...
is there something i can do? i built the loop expecially for the XP100, cause it @#$%s up the sound pretty much when it's in the signal chain...
thanks