No, buying Pro won't fix it. Some anti virus programs will mistakenly see limewire as a threat. You'll need to make an exception for LW or try another anti virus/ anti spyware program.

Also try using AVG Anti-Virus Free Edition, it's a good one that works well with LW. Also see: WARNING: Viruses on network you should be aware of!

Try uninstalling your current version of java while LW is completely shut down. Go to the add/remove programs control panel and uninstall your current version of java. Now download and install J2SE Runtime Environment (JRE) 5.0 Update 11(use the offline installer): Archive: Download Java 2 Platform Standard Edition (J2SE) 5.0 Update 11

If that fails try deleting LW's preference folder with LW completely shut down. See points 2 & 3 in this thread: Fixes for Limewire. This will reset all your option settings, so make a note of them first.

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If it ain't broke, fix it till it is!