unfortunately I have no experience with the directory reports so far, but I can explain the error to you: Your template expects the homePostalAdress to be a string while in fact it is a list (a collection of items, supposedly strings).
You could try one of the following, maybe that works:
<@attribute name=“str(homePostalAdress)”@>
# or
<@attribute name=“homePostalAdress[0]”@>
Hello Jan-Luca,
thanks for your help! I tried some variants from your examples and the errormessage disapears. Unfortunately in the report there is still no data for homePostalAdress.
I found out that the separator of the multivalue ldap attribute is $