Which OS are you using?
Try reinstalling Java. Go here:
Java SE Downloads - Sun Developer Network (SDN) & download the JRE
offline installer. Then uninstall any Java versions that you have installed at the moment via Add/Remove Programs or Vista's equivalent. Then install the version that you've just downloaded.
Restart your computer & see whether LW works.
If you still get the error, reinstall LW as well. If you have Pro, use your personal download link & if you have basic, use this link:
http://www9.limewire.com/download/LimeWireWin-full.exe
Sometimes these 'not a valid Windows image' messages can mean that there's a malware issue, but I can't find any info about a Java error being malware related.