Something IS REALLY IMPOSSIBLE. 

System 3 has been discontinued for long long time. If you still want to keep it , you need try your hard work by yourself.

here I give you some tip. Do you have the service manual if not Google it and download --see my pic. attached

You need think what is the history of your machine. Why you changed encoders? 

you change them for fixing the problem or you changed them casued your problem.

 Ahmed Abd Elmawgoud

you have good answer from below, you need check your NC program

 Solifer1

Hi , I find this alarm 408  in Sinumerik 3G manual .

Description is :Too many interpolation parametersin in  one block.

You find your controller type in the rack , there is information of this control ,is it G,M or T control also the version , Grundausfurung, GA 3 or 4  .

 #1--You can Google ROD 426  or it replacement .  I think you need to use TTL encoder , the pules / rev may special such as 512 or 1024 , other number such as 

#2--make sure the encoder is your machine problem, how can you know?

Ahmed Abd Elmawgoud

Hi;

Thanks for  help, We check and find the problem is in the main spindle encoder. It is rod 426, Can we change this type by another incremental one and change the machine parameter?

Thanks.