Sometimes companies have incredibly unrealistic expectations about job candidate performance. They search for a perfect candidate who doesn't exist. That really sounds like the case for this organization!

Another possibility is that the people in the organization who are responsible to hire for this position cannot agree on a candidate... or that the hiring manager wants someone with a completely different skillset than they are advertising/interviewing for.

What other people have said about this being fairly common with temp agencies is very true, too. This has a lot less to do with you than it has to do with the way this organization does hiring. Making mistakes, especially early on, is normal.