Whenever i create a new unit i can not select him for the next unit to be built in the game or a error message comes up what should i do

Did you edit the correct text files? Take a look at this thread (http://forums.civfanatics.com/showthread.php?t=71114). Even if it's for C3C, and you don't have that, it will still show you the guidelines.

Whenever i create a new unit i can not select him for the next unit to be built in the game or a error message comes up what should i do

It sounds like you didn't update the Units32 file.