I also had that problem and could work around by loading nls_ascii.ko module manually. It turned out that the vfat mount to access the EFI partition failed due to lack of ASCII IO charset.
So I guess the reason for the bug is the lack of a loaded nls_ascii module at the time when the partition should be prepared and mounted during the install. Regards, Thomas Wuensche -- EMS Dr. Thomas Wuensche e.K. Sonnenhang 3 85304 Ilmmuenster HRA Neuburg a.d. Donau, HR-Nr. 70.106 Phone: +49-8441-490260 Fax : +49-8441-81860 http://www.ems-wuensche.com