Limited number of Inbound Routes?

Is there a limit on the number of inbound routes?

I have a route with no 65 (called A) - it works very fine,
route no 66 (called B) sends error 404.

On changing the positions (route B has now the number 65, route A the number 66) route B is ok and route A sends the error.

inbound route limitations are more about how many and what type of incoming trunks you have vs how your system can cope with thye load eg processor / ram combinations.
One of your routes(65)is correct - check your trunk and incoming settings for 66 again.