Epson Printer & Non Epson Cartridges. Any way to override "Incompatible" screen?

The cartridges in question - 'cyan' and 'magenta' - ARE Epson compatible. They've been installed a while and were working fine. Then I had to change a completely different one - black - which ran out, and all of a sudden the printer's rejecting blue and red...?!! I've removed and then reinstalled all 4 cartridges... show more The cartridges in question - 'cyan' and 'magenta' - ARE Epson compatible. They've been installed a while and were working fine. Then I had to change a completely different one - black - which ran out, and all of a sudden the printer's rejecting blue and red...?!! I've removed and then reinstalled all 4 cartridges (all same make, btw) but that doesn't help. Instructions for cartridges says "if computer shows 'This Is Not An Epson Product' just click Yes to continue" - trouble is I can't see any Yes option on screen.
Cartridges are new, not used re-fills. I've bought from the Internet supplier before without problems. I'm stumped.
Can anyone suggest anything (apart from launching printer out the window)?
Cheers!

Update: Blimey O'Reilly, Scoundrel - I've forgotten all about the printer, old boy!
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