First of all, I want to tank you for your quick reply.. it turns out very usefull.

However, I have another problem now.. How can I make it possible to my user delete a value? Is that possible?

Hello,

I have shown a possible approach to implement this in the sample attached to this post.
Please review it and feel free to let me know if I misunderstood you or if you have any other questions.

Hello,

I think that you misunderstood my question.

My users can type the value that they want to choose o the ultracomboeditor. But I want them to can delete (with backspace key) some character that they've been type.

For example, thet want to type the value "10" but they type "100". i want to make sure that if they press backspace they can delete the last zero.

        protected override bool ProcessCmdKey(ref Message msg, Keys keyData)

        {

            if (keyData == Keys.Back)

            {

                OnKeyDown(new KeyEventArgs(Keys.Back));

                Console.WriteLine("What the Ctrl+F?");

                return true;

            }

            return base.ProcessCmdKey(ref msg, keyData);

        }

This code doesn't work.

Can you help me?

Hello,

If I got your requirements right I believe that you could use a code like the following:

        protected override bool ProcessCmdKey(ref Message msg, Keys keyData)
        {
            if (keyData == Keys.Back && (ultraComboEditor1.Editor.TextLength - ultraComboEditor1.Editor.SelectionStart == ultraComboEditor1.Editor.SelectionLength))
            {
                ultraComboEditor1.Text = ultraComboEditor1.Text.Remove(ultraComboEditor1.Editor.SelectionStart );
                ultraComboEditor1.Editor.SelectionStart = ultraComboEditor1.Editor.TextLength;
            }

            return base.ProcessCmdKey(ref msg, keyData);
        }

 Please do not hesitate to contact us if you need any additional assistance.

This code doesn't work. 

The ultraComboEditor doesn't implements the backspace key? 

My function is called but the funciton OnKeyDown doesn't do anything... do yopu know why?

        protected override bool ProcessCmdKey(ref Message msg, Keys keyData)

        {

            if (keyData == Keys.Back)

            {

                OnKeyDown(new KeyEventArgs(Keys.Back));

                return true;

            }

            return base.ProcessCmdKey(ref msg, keyData);

        }