Problem with DPP

[Ammo 7]

I sometimes use DPP to correct distortion and chromatic aberration of RAW images shot with wide angle zooms. I have corrected an image this morning but when I try to "Convert and Save" I get a "Cannot Write to File" message so I cannot export. I'm using an iMac with a recently upgraded Mavericks OS if that makes any difference. I've not had the problem before and wondering if any of you have any suggestions. Thanks