First, there's the following good news via a Detroit Pistons press release moments ago:

Newly acquired guard Jose Calderon has been cleared to play in tonight’s game at New York….He is expected to be in uniform and make his debut when the Pistons take on Knicks at Madison Square Garden (7:30 p.m.).

I have a bit of a background in immigration, as I handled all of my old firm's immigration matters and did immigration work for a large labor firm as recent as a few months ago. In order for Calderon to start "going to work" with the Pistons, he had to have a petition on his behalf for a work visa approved by the United States Citizenship and Immigration Services (USCIS). The petition had to sufficiently establish Calderon's "extraordinary ability" which was probably never an issue.

Most likely, there was never any unexpected "delay" or "issue" with Calderon's visa; it simply hadn't been approved yet. Assuming Calderon had his petition premium processed, it could have still taken upwards to 15 days for it to be approved and processed. Luckily, it only took about five.