encrypted urls, mcrypt and mod_rewrite

[Dan Rossi <php@xxxxxxxxxxxxxxxx>]

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 ?