So you are using export Field contents?
Are you doing that as a menu option or from a script?
From what Version on what OS are you attempting this? (In FileMaker 11, windows, there is one type of file that cannot be exported)
If from a script, the most common issue is the one not listed in the error message--an error is made in setting up the Path to which your script is trying to export the copy of the file. If that is possible, see this thread on $Path variables and container fields: Exploring the use of a $Path Variable in Scripts
Not quite. I have external container storage enabled in my sokution, and am trying to save a self-contained copy, so my client can have an offline version with images embedded. I'm using fmw12 on OSX maverick, not using scripts, just going through file menu.
FMP 12 was not originally compatible with Mavericks. Do you have the latest update? (See the Downloads page for a free updater.) Don't know if that will make a difference, but that's the first thing to check.
Since user account permissions can get messed up, I'd also try a number of different folders--even direct to the desktop to rule out such issues. I'd also try a different user account if one is available to use.