baffling: method or datamember not found

Have a commercial .xla add-in with a number of userforms, modules and class modules.
Used by at least 100 users without a problem.
One user however gets a compile error: method or data member not found.
This happens when in a normal module a control is referenced on one of the userforms:

MainForm.ReporttxtDescription.Text = strMessage

Now ReporttxtDescription is a VB6 .ocx based on a VB6 RichText control.
This .ocx was made to bypass security problems with the regular .ocx.

What I don't understand though is why this can't compile with this one user and fine with all the others.
Text is a property of this control and the control is fine in the references in the VBE.
The whole Office setup is bang standard with Excel 2002.
Grateful for any suggestions what could be the problem here.

RBS

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