Hi Tom,
I've found out what was happening. I had a platform wich I created in the wizard to divide the MSMCSRAM into two parts, then I copied this folder and edited the Platform.xdc file to make a new platform.
The first platform had no problem, but when I created the second platform I got the same memory space defined in default Device Memory map and in External Memory. That was the problem.
Thanks for your help.
Regards
Johannes