Why wouldn't it accept the value?
If you check books online, max server memory must be a value between 16 and 2147483647, min server memory must be a value between 0 and 2147483647. The values you set are within that range, so they're valid.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability