Importing a CCK content type with fields, that had just been exported from an identical site (did some work offline) failed with the oh-so-helpful white screen o' death (aka whitescreen, blank page).
Found no reports about this in the CCK issue queue or online elsewhere. Through cutting out parts until it worked, Agaric has been able to identify the field calling the error.
Here is the problematic field's definition, as excerpted from the export output we were trying to input into the import:
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