I think I’ve solved the problem. I copied some of the image sequences that worked into my new project directory and they stopped working as well. That got me thinking maybe it was because the file path to my files was too long and so I moved the directory closer to the root directory and, hey presto, the import seems to work fine now. I thought that kind of thing wasn’t a problem anymore with the latest versions of Windows and 64 bit OS etc. Anyway – it seems to work (so far) so I’m not complaining.
Thanks to all for the advice.
Nick