Don`t know whether you are aware of this, but in the Queue tab, if you select a queue entry, then do a right-click->Abort & Disable, then select any of the sub-options, you always get the following error:
"Illegal class typecast"
For me, this has only only started as of the 3.9 update.
http://www.metaproducts.com/download/betas/oep2091.zip
Best regards,
Oleg Chernavin
MP Staff