If you ever bump into this message when opening, refreshing or saving a document, there’s probably a field on your document breaking the 32K or 64K limit of the maximum field size for simple text fields.
To be more specific, the limit is 32K for fields with IsSummary flag on, and 64K for other fields (I did some extra research :-)). But, more importantly, what field should you look for? What can cause this overflowing fieldbucket? Aim for a @DbLookup or @DbColumn in a computed or computed for display field.
I ran into this error and it took me a couple of hours to find the cause. Just to realize that I had this error before. Time to document this :-). In my case a computed for display field was used as a source for choices in keyword lists. The field did a lookup for a huge list of people and this list became too big. I solved it by splitting it up in different fields, then joining these values again in the choices of the keyword list.