Verifique se a string de conexão no arquivo web.config está correta
<add name="STRING_CONNECTION" connectionString="Server=[SERVER];Database=[DATA BASE NAME];Uid=[USER];Pwd=[PASSWORD];" providerName="MySql.Data.MySqlClient"/>
<add name="STRING_CONNECTION" connectionString="Server=[SERVER];Database=[DATA BASE NAME];Uid=[USER];Pwd=[PASSWORD];" providerName="MySql.Data.MySqlClient"/>