Manolo Gonzalez-Estay, a garden-variety activist (he does not seem to be affiliated with any particular group) challenged the ballot measure in court because it would deny services such as welfare and in-state college tuition to illegal immigrants.
Faster than you can say judicial activism, the Court struck down the measure because it supposedly violated a state rule which limits a ballot initiative to only one subject.
Follow this explanation from an AP article that came out a few minutes ago,
"According to the ruling, Defend Colorado Now touted the possibility of reducing taxpayer expenditures by restricting illegal immigrants' access to services, as well as the goal of restricting access to services." Colorado Court Rules Against Ballot Measure by Jon Sarche AP 6/12/06
It restricts access to state services for illegal immigrants and it...restricts access to state services for illegal immigrants.
I'm not sure how that's more than one subject but these namby-pamby judges seem to speak their own looney language these days.
Here's the email page for the court.