I have answered my own question... Stupidly I'd let a Mac create an iTunes library on the same shared drive. I just deleted all the small Mac files it left behind and hey presto, everything works perfectly again. Strange.
Thanks for the suggestion, I downloaded a trial and it looks great. Helped me identify the issue I have... couldn't create a directory... need to check parent folder permissions. Any suggestions for best way to do this? Again, please excuse my ignorance.