Disabling Control Causes Crash

I'm working with Excel 2000 on Windows XP machines. I have the following

Private Sub soInputBox_KeyDown(ByVal KeyCode As MSForms.ReturnInteger, ByVal Shift As Integer)
If KeyCode = vbKeyReturn Then
PushScreenUpdateState False
clearAllData
loadAllData
Worksheets("Main Screen").Activate
PopScreenUpdateState
End If
End Sub

Private Sub loadAllData()
soInputBox.Enabled = False
End Sub

The idea is this: the user can either type the value into the text box (soInputBox) and then click a button, or type the value into the box and then hit enter. They will both do the same thing; set in motion all the functions that load a bunch of data, etc.The code for the event handler for hitting enter is shown above. Inside of the loadAllData function, I disable the text box. What seems to be happening is that after the soInputBox_KeyDown function exits, Excel crashes. If I comment out the line to disable the text box, Excel doesn't crash. My question is this: is this a known problem, and is there a known workaround? I would like it so that the text box is disabled so that the value that was input cannot be changed accidentally during the rest of the programs execution, so if there's a way to change the control to be unmodifiable instead of disabling it that would be a reasonable alternative.