Over the last days I encountered the following error on my Sun Ray DTUs after trying to log in via dtlogin:

Workspace Manager: I/O error on display:: :4.0

There were also quite a few other errors in the SUNWut logs (eg. PAM_CONV_ERR), which got me on a wild goose chase at first.

Lastly, I found out that the problem was the $LD_LIBRARY_PATH environment variable that was set via /etc/profile. Despite fixing the problem, I couldn’t find the problematic library yet.