I updated nethserver-guacamole recently to provide Guacamole 1.5.0.
Which version do you use?
rpm -qa nethserver-guacamole
EDIT:
If you have updated to nethserver-guacamole-0.0.1-7 you may try a downgrade:
yum downgrade nethserver-guacamole
EDIT2:
I can’t reproduce the “FileNotFound” errors.
Do you also get the segfault error in /var/log/messages as explained here?
guacd[19074]: segfault at 0 ip 00007eff00efba54 sp 00007efeee813718 error 6 in libc-2.17.so[7eff00e6c000+1c4000]