Try 'F1'. The special keys work in older versions of Win32::GuiTest.
The code to allow IsKeyPressed to understand a parameter of 'A' was added in version 1.50.2-ad. You probably are running 1.3. Try this to see:

perl -MWin32::GuiTest -wle print($Win32::GuiTest::VERSION)
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See my reply to Grandfather, above, for the correct table of special keys that work with 1.3.