Might this have been a file originally inserted as an object in FileMaker 11 windows? (You don't tell us what version you are using nor on what platform).
Sorry! This is Filemaker Pro 13 on Mac.
And not a file where the file was inserted as an object and then converted to .fmp12 file format?
Can you export other files from this container field in other records?
Can you try the following:
Delete the file from the container. then Insert it again into the container field, then see if you can export it.
Create a new record, insert a copy of this file into it and then try exporting from it.
If none of the above works, you may need to take this file or a very recent back up copy and check it for possible file damage by running a recover on the file.
My artist just came up to me and said she found out where in the file there was corruption.
No filemaker issue, it was an issue with the file.
Thanks for your help!