Can you tell me which version of FieldWorks you are using? I think
this is a compatibility error. I am guessing you need to install the
latest version of FieldWorks.
As an alternative, you can switch to the Configured Dictionary View
and then use File : Export : XHTML to create a file and then use the
stand alone application Start : PublishingSolution. Once it launches
use File : New and supply the name of the exported XHTML file. You can
continue processing from there if you have Flex 5.4.1. (Versions
before 5.4.1 have no XHTML export option).

I recently upgraded to v. 6, so the version shouldn't be the problem.
I would be happy to use the stand-alone, but I'm not sure where I get
it...can you explain for a very technically challenged linguist? (To
this day, I am not even sure how I found or installed the Pub.
Solutions plug-in, b/c when I looked for it on sil.org I could never
find it, and whatever I did involved some torturous non-obvious [to
me] process.)
Thanks a lot!!
Lynnika