Import Contacts fails to import majority of contacts, claims custom field error but doesn't say what custom field

Having some weird issues with the Import Contacts in 4.1

Trying to import 1000 rows of data. Basic name, address and about 8 custom fields, mostly alphanumeric and text custom data.

CiviCRM said prior to import that 999 rows contained valid data.

After import, only 32 rows were actually imported. Not sure what is going on here. The 32 rows imported did have custom data, so the lack of custom data is not a reason they succeeded when the others failed.

The rest of the batch were errors, but the attached error document doesn't say what custom field is the problem. (note that in the attached data file I have deleted the actual data for the sake of privacy, it is the blank error itself that is concerning).

Also it's notable that although there were over 900 errors, the error file only contains ~200 error rows.

If you want to poke around on the website or get the data, let me know.