Based on a google search, SBC could stand for Single Byte Character, part of SBCS - Single Byte Character Set, in which character encodings use exactly one byte for each graphic character. There is also DBCS (double), TBCS (triple) and MBCS (multiple). SBCSs are limited to 256 symbols and are useful for character sets that don't have many symbols or accented letters, like European languages. Chinese, Japanese and Korean fonts are usually MBCS because they have large numbers of characters and symbols.
If you're working in Japanese text, my guess is the font you're using is a MBSC and your client wants one that is a SBCS.