Posted 15 Jan 2013
Link to this post
Actually those operators are not applicable for type String. They can be used for values that can be compared through the ">", ">=", "<" and "<=" operations.
Explore the entire Telerik portfolio by downloading Telerik DevCraft Ultimate.
I am not sure how have you done your implementation so that to filter with the combobox, have you used approach similar to the one described in this help article?