TheFakeSheikh's advice is mostly there. Specifically what you need to do is find the Receipts folder & remove the install limewire.pkg file, before the system will allow you to install an earlier version. Receipts folder sample image

We'd actually recommend you install LW 4.16 rather than 4.18 but that's up to you. http://www.gnutellaforums.com/downlo...downloads.html but you only need to see step 1. Steps 2 & 3 are only if you actually used LW 5 & wanted to move back to LW 4.

I have checked my receipts folder, and done a search for that name, and nothing has come up. I tired downloading and installing 4.16, and the exact same thing happens.
Does this mean it is a problem with my particular computer, and not limewire?