Update: Ignore this. I just saw that the problem may be related to (access to) data
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I think it's obvious that you'd have to debug this at the client, if you can. I don't know if you've made the determination on whether this is related to data related, or to something else.
I'd try to remove any references on the ControlSource of the editbox giving the error, and see if that works. If yes, then clearly the problem is data (or dataenvironment) related and you can focus on that path. Otherwise, it may be the class definition, or the resources available at the time the second editbox is instantiated.
My 2c.

>Running into something weird. In an inherited application, I just changed a table to have a single memo field instead of two char fields for notes, and replaced the pair of textboxes on the relevant forms with an editbox. There are two forms involved. The first is pretty much display-only, shows a grid of all records on one page and detail of the currently selected record on a second. A button on that form instantiates a form class for editing the record.
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>When I test here, all works as expected. Both forms open and show the right data. At the client site, the display form is fine, but instantiation of the editing form class fails with error 1736 and the message says "Error instantiating the object EDTNOTES." That's, of course, the newly added editbox that replaced the two character fields.
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>I gave the client a separate EXE to make the database change and he ran it before testing the updated application. The fact that the first form opens correctly and shows the data correctly means the table was properly updated.
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>I had the client send me the updated table and tested with it here and both forms work as expected.
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>The only differences I can think of are:
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>- the client is using Windows 10, while I'm on Windows 7 (but that he could send me the modified table means we're not dealing with virtualization);
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>- the client has the data living on a mapped drive on a server, while I'm testing locally. Given that things are working generally, I don't see how this could matter.
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>I'm at a loss. Any ideas?
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>Tamar