Jira is not working

[Chris Greeno]

Failed to create new entry for issue 42003, nextId null and custom field 12000 because conflicting data already exists

[Radu Dumitriu]

Muddy Waters, remember? Got my mojo working but it just won't work for/on you.

[Andy Brook [Plugin People]]

Consider re-titling the question, its hardly accurate. Im not exactly sure what you are trying to say, how this data got there, with what.

From the scant information provided it appears to be related to custom fields in some way, the type of this custom field might be significant... Explain your usage, plugins, versions when posting questions to get useful timely responses.