encrypted urls, mcrypt and mod_rewrite

Hi ive been trying to find answers with no luck. I am sending a urlencoded encrypted string made with mcrypt. what is happening is there is somehow special characters that mod_rewrite doesnt like so it wont find a regex match properly with this rule RewriteRule ^feeds/(.*)$ refer.php?$1 [L,QSA] Any ideas what it could be doing ? The strings are also quite random, so it will work sometimes for a particular url then other times not ?