cant install sql server 2008 r2 standard, giving me error when checking the operating system rule

keep getting the following error when im trying to install SQL server 2008 standard r2 on a windows 2008 server r2 standard OS!
on the Installaion Rules page i get an error on OPERATING SYSTEM SUPPORTED FOR EDITION
it FAILS
when i click on status FAILED, i get the following response
Rule "Operating system supported for edition" failed.
This SQL Server edition is not supported on this operating system.
See SQL Server Books Online for information about supported operating systems for SQL Small Business Server edition.

As stated, im running Windows Server 2008 R2 Standard, not SBS
Any ideas?
(see the 'view detailed report' option below)


InstallFeatureSpecificRules: SQL Server 2008 R2 Setup configuration checks for rules group 'InstallFeatureSpecificRules'  
  EditionRequirementCheck Checks whether the SQL Server edition is supported on this operating system. Failed This SQL Server edition is not supported on this operating system. See SQL Server Books Online for information about supported operating systems for SQL Small Business Server edition.