Claas Atos 350 problem

[Ervin57]

I have a claas atos 350 from 2015
The tractor have 4100hour
Today get 1 error code: T15
when I release the parking brake, the stop light flashes and beeps
what does this code mean?
When i

 

[Let’s Go 1872]

There was a mod for the hand brake on the early first generation atos’s , if it hasn’t been done it may be something to do with it