I have worked around this issue by disabling Avast temporarily during the installation. Then re-enabling Avast allowing Avast to quarantine the Openlp executable and then restoring and adding an exception by right clicking in the quarantine. It seems to take a while for Avast to accept that it is an exception but after a bit of fiddling around it does work with Avast being enabled.
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I too have reported the false positive...
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-Paul