MATLAB: Error message when compiling App: “Warning: A value of class “char” was indexed with no subscripts specified.”

app designererrorMATLAB

I have written a fairly long (>6000 lines) app. Can someone please explain what this error means, how to locate the offending code, and how to fix it? The full message is "Warning: A value of class "char" was indexed with no subscripts specified. Currently the result of this operation is the indexed value itself, but in a future release, it will be an error."
Thanks!
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