License error: missing serial number

[spokojnie55]

Hi, I have two QNAP TS-230s, both run the same software versions. On one of them minimserver (now with full licence) works perfectly, on the other one it didn't before and I can't add the licence as it claims that: "License error: missing serial number." I can't get it to work, I uninstalled and installed it again several times, the "Licence" tab is basically unaccesible. Any idea how to get it to work? Thanks.