ado.net error : String[2]: the Size property has an invalid size of 0

I am getting below error while executing stored procedure from C# (Ado.net, entity framework)

String[2]: the Size property has an invalid size of 0.

SqlParameter input1Parameter = new SqlParameter()

            {

                ParameterName = " input1",

                Direction = System.Data.ParameterDirection.Input,

                Value = input1,

                SqlDbType = System.Data.SqlDbType.VarChar

            };

SqlParameter input2Parameter = new SqlParameter()

            {

                ParameterName = " input2",

                Direction = System.Data.ParameterDirection.Input,

                Value = input2,

                SqlDbType = System.Data.SqlDbType.VarChar

            };

SqlParameter output1Parameter = new SqlParameter()

            {

                ParameterName = "output1",

                Direction = System.Data.ParameterDirection.Output,

                SqlDbType = System.Data.SqlDbType.VarChar

            };

Old query: throwing error as “String[2]: the Size property has an invalid size of 0”

var result = Database.ExecuteSqlCommand("exec schemaname.stored_proc_name @input1, @input2, @output1 OUTPUT", input1Parameter, input2Parameter, output1Parameter);

Updated Query: Fix : removed exec

var result = Database.ExecuteSqlCommand("schemaname.stored_proc_name @input1, @input2, @output1 OUTPUT", input1Parameter, input2Parameter, output1Parameter);