Project Coding mask error

Hi,

While I'm going to create a new coding mask, system is throwing an error "Edit screen is "3" too long" Message No. CJ627.

The coding mask what I want "DU/XXXX/0000-XX-XX-XX-XX" which is 24 characters but still I'm not able to understand why system is throwing error.

System only allows me create up to 21 characters, why is it so?

Thanks,

Soubhagya