Thanks for your input. It looks as though I was just being stupid though!

The code was running without error and I did have bulkadmin rights, but when I did a SELECT from the destination table, the column containing the image (attachment) was just showing as blank whereas all the other rows in that table were displaying a load of hex for the attachment so I assumed the file wasn't being imported. When I actually went and bothered to check in the UI of this application, the file was there.

It seems as though the hex appearing in the column depends on the type of file being imported. xlsx, txt and doc files are represented with hex. Xls, pdf and jpg files show as blanks. It would be interesting to know why this is the case - perhaps something to do with system registered file types? - but happy that my problem wasn't actually a problem!

Thanks again for taking a look at my question Sigerson!