[Plugin: Ajax Categories Posts Dropdown] “Select a category first”

I’ve tried the Ajax Categories Posts Dropdown plugin now on two sites, one WP 2.7.x and one 2.9.2 I’ve tried it as a widget and straight into the template file.

In all instances the top dropdown displays just fine and the categories appear with the number of posts listed. However, the second dropdown never changes. It always says “Select a category first”.

I’ve tried deactivating all plugins but this one and it does the same thing — it’s not a conflict.

Any ideas on what could be causing this? Has anyone else had this problem?