c# richtext存入文字+图片至数据库，读取时报文件格式无效错误

//将richtext中文字+图片存入数据库
this.rtbText.SaveFile(mstream, RichTextBoxStreamType.RichText);
mstream.Position = 0;
 SqlCommand cmd = new SqlCommand();
 System.Data.SqlClient.SqlParameter[] pram = new System.Data.SqlClient.SqlParameter[] { };
 cmd.Parameters.AddWithValue("@project_content",mstream.ToArray());
string sql = "insert into project values('" + cbbHospotal.Text + "','" + cbbType.Text + "','@project_content','未确认','待开发','','" + AllStatic.userName + "',getdate(),'','" + label2.Text + "')";
 int i = sl.ExecuteNonQuery(sql,pram,CommandType.Text);

//从数据库读取至richtext
 byte[] bWrite = (byte[])(dt.Rows[0]["project_content"]);

 if (bWrite != null)
 {
 using ( MemoryStream mstream = new MemoryStream())
 {
mstream.Write(bWrite, 0, bWrite.Length);
mstream.Position = 0;
//将stream填充到RichTextBox
this.richTextBox1.LoadFile(mstream, RichTextBoxStreamType.RichText);
                   } }

报错，文件格式无效

debug一下，看一下从数据库取出的数据是什么格式的