Reference Frustration

I am very frustrated today.

I have a potential job offer on the table from the job that I interviewed for on July 2nd. They called me this morning and told me they had been trying to get a hold of my references since July 6th. That is 3 whole weeks! I could have had this job 3 weeks ago but my references seem to be avoiding her phone calls.

One reference, a previous boss, I am going to take off my resume completely. Her title looks good, but she is just not accessible.

Another reference, a coworker/supervisor has been able to get in touch with my potential employer and was actively trying. Thank you!

The last one seems to be avoiding all contact. I wonder why...

Have you ever had problems with references? Who are the best people to use?