Thanks, yes I've now realized that that is the problem.
I have a number of WorldView images from Digital Globe. They are labelled as R1C1, R2C1 etc. and all end in P001. I have a metadata file (.imd) but only for P001 and not for each individual image. I have tried mosaicing all the WorldView images together to form a single file for P001 but am still having trouble reading the metadata file (error: Failed to getmetadata).
I can view the metadata in ERDAS.