I just tried the OP's test code again, this time on Mathematica 10.1 under Win7 64-bit. It worked again.
One suggestion is to modify the Export statement to be so:
Export["image1.fits", d, "Data"]
Here's a reminder that I use: (* !! FITS: Export "Data", Import "RawData" !! *)
Hmm... I still get the error on Mathematica 10.1 under OSX Yosemite, even using the Export["image1.fits", d, "Data"] line.
I can't seem to find any more documentation on this issue.
Thanks for the reply though.
Did you ever find the solution? I have the same error, even in the help documentation. I'm on Mathematica 10 - I've never encountered the error before.