CCK field migration reproducibly results in server error on node display
We have now identified the source of the error. The content-migrate process seems to sometimes generate invalid display settings for fields. We have now seen this for two different fields. To identify the offending field, we did the following to debug:


if possible, (you getting at least a drupal error) get a call stack, so that the offending field type and field name can be searched for (grep for 'field')
to repair offending settings: go to admin/structure/types/manage/&lt;data type&gt;/display 
set each field &lt;hidden&gt; in the Label column (yes that is odd, but I guess this setting is enough to trigger generating fresh display settings)
Save
set each field back to original Label settings
Save


If you want to find the culprit without stack trace, one could switch each field off, and reload the content. 

I am not sure about the reason for why this works, but I suspect serialized data. Drupal uses a lot of serialized strings to store settings in the database, and the deserialization might not be robust against corrupted settings. I don't think this is really a bug in the migration code, but corrupted settings can occur at any time.

So I guess it might be a good idea to re-generate settings, in any case of a display error of custom content.