[argyllcms] No protocol specified and no displays found

I've got a strange problem.

I have previously profiled my monitor with no problems.  Today when I
try to load the profile I get the following error:

No protocol specified
Dispwin: Error - Unable to open the default display

Running dispwin with no arguments results in it telling me that there
are no displays.

I'm not doing anything differently to what I've done before and it
used to work.  Any ideas?  I'm on linux, running as root.

Cheers

Peter.

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