Sorry for not being clear. The table in my previous reply was an example of a lookup table that would return an error.
From the MSDN website, about the behaviour of LOOKUPVALUE in case of duplicates:
"If multiple rows match the search values and in all cases result_column values are identical then that value is returned. However, if result_column returns different values an error is returned."
In other words, you are trying to answer the question whether Jan is employed. LOOKUPVALUE will work fine if it finds the same answer twice, but will return an error if finds two different answers.
So, the main issue is you have ambiguity in your real data, and the first question is how you want to handle this ambiguity.
A business rule to solve this issue could be the following: employee X must be considered employed as long as there is no record in Verzuimloop where Employed = 0.
In that case, you could filter Verzuimloop accordingly and check that LOOKUPVALUE returns BLANK.
