Tesco believes that this has a compatibility problem with its system, which can be very easily fixed if customers follow some instructions to reset their browsers.

BBC: Tesco Bank offers refunds pledge

Bug-for-bug compatibility is a problem, but breaking backward compatibility would be a much bigger problem, so even as the lowest layers of the operating system are revised and rewritten, the layers that applictions talk to (the application programming interface, or API) are carefully tested to ensure that no changes are visible to the application.

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This is the real issue behind all sorts of problem of compatibility and delays (especially in the UK).

BBC: Viewpoint: What 4G means for you and your phone

The EC itself has already said "we have a problem with the compatibility of minimum pricing plans under community law".

BBC: Minimum pricing having a difficult birth in Scotland

The EC itself has said "what we can say is we have a problem with the compatibility of minimum pricing plans under community law".

BBC: Scotland

To overcome the problem of backward-compatibility, modern x86 chips such as the Pentium are able to take x86-style instructions from old software and split them up into several smaller micro-operations which lend themselves better to performance-enhancing trickery.

ECONOMIST: Transmetamorphosis

The management problem lies not just in the quantity but also in the compatibility, or lack thereof.

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