Custom message box issue

We have a custom messagebox. Due to the fact of company logo, colors etc. Can't get away from that.
the code on the form is

Private Sub Form_Load()
    On Error GoTo ERR_SUB
   
        Me.lblMessage.Caption = Me.OpenArgs 'Value which is passed in
       
Sometimes the data is large (number of characters) I want to pass. I get an error that the OpenForm Action was cancelled.
I'm not sure if this is due to the string limitation (255) or that it's displaying in a label or both. The individual lines have vbCrLf so the display is nicely formated. Is my limitation the string length? The caption length? Should I use a textbox? Or should I change it to a ListBox?

Thanks.