Validating Textbox On Userform And SetFocus

I have two userforms. When the user chooses the choice "Other" in the userform frmTradeSickOther, another userform called frmOther will be called. At this point, the user will enter some required comments in a textbox (called txtOther) and click the "Add Comment" button. If the user does not enter anything, a prompt will inform the user to type something in the textbox.

My problems: Once the user clicks okay to the prompt, frmOther is called back. When it's called back, I want the cursor to blink in the textbox. Eventhough I have SetFocus on the textbox, it does not work. I don't know why.How do I prevent the user from just hitting enter (i.e., accepting blank lines as comments) and bypassing the commenting part. The code below accounts for hitting enter once (i.e., one blank line), but not multiple times. How do I do this?

Here is what I have when the user clicks on the "Other" choice in frmTradeSickOther:

Code:
Private Sub optOther_Click()
Unload Me
frmOther.Show
frmOther.txtOther.SetFocus 'This gets the cursor to blink in textOther when frmOther is called.
End Sub

Here is what I have when the user clicks the "Add Comment" button on frmOther:

Code:
Private Sub btnAddComment_Click()
On Error Resume Next
txtOther.Value = Trim(txtOther.Value) 'This is to make sure spaces aren't accepted as a comment.
If Me.txtOther = vbNullString Then
Me.Hide
MsgBox "Please enter the necessary information.", vbInformation, "Required Field"
Me.Show
Me.txtOther.SetFocus 'Here is where I set focus on txtOther.
Exit Sub
End If

'Everything below is to add comments automatically to each cell when a value is changed.

Application.CommandBars("Cell").Controls("Delete Comment").Enabled = True
If Not ActiveCell.Comment Is Nothing Then
Application.CommandBars("Cell").Controls("Edit Comment").Enabled = True
Range(curCell).ClearComments

[Code] .......