将字节数组转换为字符串时获取'System.OutOfMemoryException'

code snippet:

//byte[] myByteArray = byte array from database (database BLOB) 
myByteArray = (byte[]) ((dbCommand.Parameters["parameter"].Value));

string myString =System.Text.Encoding.UTF8.GetString(myByteArray);

Xmldocument doc = new Xmldocument();
doc.Load(myString);
//byte[] myByteArray = byte arr