Student license issue - ST4

Hi all - I'm currently using ST4 and need to refresh my key. I registered again and got an email with a key. Unfortunately, when I enter the key over the License Utility, it says: "Key not valid for this machine". I mentioned that the new key came together with a link to ST6, is the ST6 key compatible with ST4? What I was also wondering about is, that I have a Lisence.dat file in the program folder? Thanks in advance. Regards, Oliver