Hi, try tu run JOSM 7000 with 10.6 and Java version "1.6.0_65"
"Prime size must be multiple of 64 an can omnly range from 512 to 1024 (inclusive)"
I vaguely remember I had the same problem a long time ago. I believe you have to turn off all secure calls to the OSM server.
Under the "advanced preferences" you should replace all https to http. I hoped to find something on the archives of the josm-dev mailing lis t (where I think I asked that question a long time ago), but it is not easily seachable.