Google WebMaster tool.

HTTP errors : 2,296
Not found :422
Unreachable URLs :476
Anyway i can fix this?

You will never have 0 in most of these fields.

Bad links get into google all the time (via others linking to you incorrectly, or a typo, etc etc). eventually, they will drop out of the index.

The point is to observe the data. click on them. if you think they SHOULD exist, you need to figure out why it 404'ed.

http errors and unreachable urls tend to come from server downtime.