Cannot open windows when using a node

[xaviergp]

Hi! I have an issue:
When I try to open a node the systems asks for a password. It does not accept my password, but if I simply press return 3 times it looks like it gives me access to the node. However, an error message says that x11 could not connect to the node:

[17:51][1.85][-102%]xaviergp@openmind7:~$ srun --x11 --pty --mem=1G bash
The authenticity of host 'node012 (172.16.20.12)' can't be established.
ECDSA key fingerprint is b8:77:68:03:fc:8d:a4:5a:64:87:7a:9a:10:10:9a:90.
Are you sure you want to continue connecting (yes/no)? 
xaviergp@node012's password: 
xaviergp@node012's password: 
xaviergp@node012's password: 
srun: error: x11: unable to connect node node012
[17:52][14.31][-88%]xaviergp@node012:~$

Once I am in the node I cannot open windows such as Matlab. It seems like the reason is that x11 is not working well in the node:

[17:52][14.31][-88%]xaviergp@node012:~$ module add mit/matlab/2016b
[17:52][14.52][-88%]xaviergp@node012:~$ matlab
MATLAB is selecting SOFTWARE OPENGL rendering.

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Is there any solution?
Thank you!
Xavier.