AVI can contain lots of different stuff, just like a bowl of fruit. Kiwi, orange, pear, grapes, apple, mango, peach, etc.
The AVI is not suitable, wrong codec. You need MS DV AVI type2. Or, PR works only with apples (not MAC's) but hates the rest, it is allergic to the other stuff. Convert to the correct format. Use G-Spot to find the current codec and then search Google for a suitable converter.
This ARTICLE will give you some background on AVI's (and MOV's and WMV's and MPEG's too). It all depends on what is inside that/those "wrapper(s)."
It will also tell you how to "peak" inside that wrapper, and gather details on the CODEC. That is very likely your problem.