Hello Matthias,
do you mean the "Import Request" button (instead of the "Import All Requests" button)?
Try to revoke from authorization S_CTS_ADMI from field CTS_ADMFCT the value IMPS.
Just for the record: the authorization help on S_CTS_ADMI shows the following:
"Do not use the authorization "IMPT" any more. Instead, grant one of the specific authorizations IMPA, IMPS, TADD, TDEL, TQAS, or TADM.
"IMPA"
Import all transport requests in the import queue
"IMPS"
Import individual transport requests into the target system"
Best regards,
Laszlo