I've been having some of the same problems posted here specifically freezing crashing having to force quit losing files that were downloading a long time and then reinstalling to try to solve problem and then the problem occuring again and again. I'm using OS 10.4.9. Looking for simple clues I found that it says the current version of Acquisition must use Java 1.5. I had already installed that, however, I discovered that even though I installed Java 2 SE 5.0 (Java 1.5 is inside this somehow) it retained Java 1.4 for backward compatability I assume. This brought me to an answer that so far has cleared up the problem. You have to open the Jave 2 SE 5.0 folder (Look in utilities) and click on preferences. Under General drag 5.0 to the Java Applet Runtime Parameters (a 0 appears) then drag 1.4 to JARP (a 1 appears). Close and save. That's it. Hope it works for you as did for me.