Subscribe by email hanging

I have been using subscribe by email on a site but recently it has been taking over a minute to manually subscribe someone to the list. It also had my server running at 100% cpu all the time. So much so i have had to disable the plug in. Once i did this the performance of the server and the site returned to normal. Has anyone else had this problem or know what the cause could be? I did get an unresponsive script error at one point as well.