#6 Cannot enter aggregate attribute value

[Anonymous]

In the Data Creator, I cannot enter a series of values
for a simple-typed aggregate attribute.

I have an attribute OPTIONAL LIST [0:?] OF STRING, and
would like to insert ('a', 'b') as its value. However,
if I do this I get the error message: Can't read your
input: "An error of type CONDITIONS:SIMPLE-READER-
ERROR occured, arguments (:FORMAT-STRING \"Close
parenthesis at top level.\":FORMAT-ARGUMENTS NILL)"