I spent a bit more time on the machine yesterday, so a bit more information.
The messages that appear are not all the same - the last digit of the address varies. I have seen 0x28000A and 0x28000B as well as 0x280001 noted in the original post.
The 0x280001 message comes up when I press the "Mech align" button. IIRC there used to be an information message came up prompting the carousel to be positioned at station 1 before confirming using the "Mech align" button.
I can align the axes & the toolchanger and then clear the error messages, so am assuming that I have some corrupted message files somewhere ?
The control appears to be operating from a 1GB Compact flash card - I can see no HDD. The card shows a directory called "Mustang" - is this the CNC operating system ?
Can anybody point me in the direction of the message or info files, or suggest how I can repair or reformat the files, please ?