The pmr will only work with AIR not Co2 as it can damage the electronics and the workings of the marker. Did you not read the manual before using it. If I was you I would take it to a paintball shop and get them to check to see if you have permant damage.
didnt get a manual with it so didnt know, it should be fine as i didnt even fire it just gased it up but will get it cheaked out anyway. dont suppose you know where i can get a manual from to download do ya??
Here is a link to manual which will tell you everything about your pmr Proto Manual
The main reason for not using Co2 is that it is stored in liquid form then it is changed to a gas which if the liquid gets into the internals of the marker will damage them. High Pressured Air(HPA) is stored as a gas and will always remain as a gas it does not damage the internals.