CSV import fails with AJAX HTTP field.attach.inc error

Hi

Previously successful csv file imports suddenly started failing with the following error

An AJAX HTTP error occurred. HTTP Result Code: 200 Debugging information follows. Path: /batch?id=68&op=do StatusText: OK ResponseText: Fatal error: Cannot access empty property in .../modules/field/field.attach.inc on line 198

I don't know what happened as the same file was being imported successfully.
THe imports are successful if I replace the data in the file with nothing but numbers. However, adding any text causes the import to fail with above error.

I'm generating the csv from a libreoffice calc spreadsheet and saving as UTF8. The same error occurs under 7.x-2.0-alpha3 as well.

Help anybody

emk