Motorcycle Repair: Pops out of gear into neutral @ 5000rpm, oil viscosity, selector fork

Question
What would cause a bike to pop out of gear when i hit 5000 rpm in 2nd gear?

Answer
Could be any number of things, but typically it means a bent selector fork.  This is usually a large job.  Does it feel like the gear is engaging positively?  You can change the oil and see if it makes a difference; use the manufacturer's recommended oil viscosity.  Good luck,  Jan