I know that some users have experienced problems with external lookups in V11 and you should find some posts on the forum regarding that.
Assuming that you're not running V11, the first step is to be clear in your own mind, exactly what is happening.
Have you upgraded to a new version of Monarch, have any changes been made to the model recently, have any files that you're linking to, changed name or moved to a different folder?, Is the data in your lookup files coming from a different source, Is someone new keying in data?
If you're successfully pulling information from a file using a lookup but, some of the fields that you're importing appear blank; is it always the same fields?
If the problem is consistent and repeatable i.e. always the same fields missing, you can start to home in on the specific problem.
A common cause can be incorrect field types. If you are pulling in character data but you have the field type set to numeric or date etc. the field will appear blank.
If you're pulling data from multiple files that should all be in a common format; are they all in the correct format (field names all correct, field types all correct).
Do you have trailing spaces in the main data table but not in the lookup files for the linking field, or vice versa ?
I'm afraid these are all very general but, it's difficult to be any more specific without a little more detailed information about your problem.
Hope it helps anyway.
I checked to make sure the model and source document hadnt changed. What is thoroughly confusing is why some fields are importing from a common column and some are not. i would be glad to share my model and source doc's....I've closed and re-opened the project...I've closed the model and reopened. I'm stumped because on the surface I dont see anything in the source document which would inhibit the full external import. tks