Grinding Gears

I was out riding yesterday for about 2 hours and everything was working Perfectly. I shut the bike off (1994 cr125) and let it sit for a while. WHen i went to roll it forward, neutral would feel almost like it was engaging like a gear, but i knew for a fact it was neutral. Also 2nd and 3rd gear would not engage and grind VERY bad, Even when i engaged the clutch to shift past them from 1st to fourth they would grind! PLEASE any help at all would be more then i have now! thanks

Side note: I used a different tranny oil for the first time, but it was a two stroke oil. Could this have cause them to just slip out of place?

ha ha if i would have done that, then i would never have the guts to post it. I meant 2-cycle tranny oil