buildid:
2.6.0.v20100330-0630

steps to reproduce:
1. new a dataset
2. new a table binding with the dataset
3. add a group for the table, do not close the new group dialogue.
4. in the new group dialog, add a group filter, condition:
   choose either column, condition: equal to, 
5. try to choose <select value...> for the condition.

expected result:
value can be displayed after choosing select value

actual result:
error pops up

more info:
-this works in release 2.3.2.1.
-if i save and closed the new group dialog first. then reopen it for adding filter, it works.
fixed it.
verified in 2.6.0.v20100408-0630
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