Hi,
Its because you are using a latin collation whihc is not comaptible with Persian unicode characters. mojoPortal sql install scripts do not set any charset or collation, you need to set the collation that suits your language on your database before running the setup scripts. Probably your sql server has a default of latin, you could change the server default before cresating a database or you can change it on a new db before running setup. If you waited until after runnning setup then you would probably have to change it manually on every table and column. See this article Non-English Languages and SQL Server or do some googling to learn more. If you google for the error "Cannot resolve the collation conflict between "SQL_Latin1_General_CP1_CI_AS" and "SQL_Latin1_General_CP1256_CI_AS" in the equal to operation." you will find lots of results that may help you.
Hope that helps,
Joe