Dan,
Are you on a DF or DF+ or XF? I found this:
"It appears that there has been a minor electrical problem in the body and as such it is not properly communicating to the leaf shutter...While this requires repair, there is a workaround. You should be able to capture normally if you disable the leaf shutter and just use the body's focal plane shutter. You can do this by changing the custom functions for "Shutter in M mode" to Only Focal Plane. On the body dial this is CF-18 that you would change to 2. Just besure that you activate the custom function set that you modify. If you modify set A be sure that set A is activated... This is the most common mistake people make when setting custom functions."
On a Phase One support forum. It was for a different issue, but does seem to address the issue of turning off the leaf shutter and only using the focal plane shutter.
If you are on a XF, I assume there is a similar function, but could not find anything in the "user" manual Phase One has published on their main site, i.e. there is no list of the custom functions. But hopefully a XF owner or dealer can help there.
Sorry to see you are having an issue.
Paul