Just to conclude this thread, you might wish to know the reason for this problem, and one possible solution. This is what was said on the Phase 1 forum that Doug pointed me to. This is not an issue when importing into LRv5.
"It seems that Lightroom 4 has a bit of a bug in regard to Keyword handling.
In Capture One 8 we've introduced the standard for including Keywords in processed files. This includes Hierarchical Keywords which was not available in Capture One 7.
When Capture One 8 process' an image without any keywords, the field where they would reside is still present in the file but is of course blank. When importing into Lightroom 4 this blank field is what stalls the import process. Lightroom 5 does not have this conflict as it correctly skips the field if no Keywords are available. As should occur. No issue with the files, no issue with the thumbnails, just a conflict with proper handling of Keywords or a lack thereof.
So, as an immediate solution to those with this issue, please simply add a Keyword to the processed files in Capture One 8 and Lightroom 4 can then complete the import process as there is data present in the field."
Ian