Thank you Colaxais & AcceptWorldcoins for your responses.
Using the old wallet could possibly resolve my problem.
I got the network alert when launched v0.8.6.1-30-g7ca106d-beta version from your link.
Is it safe to use that version? No hardfork occurred since or is going to?
edit: I compiled also v0.8.6.2-g55c5572-beta and got the same alert.
If I remember correctly, 0.8.6.2 is the oldest wallet you can use. 0.8.6.2 is fine though, as v1 and higher are optional right now.
Sorry I'm not sure about compiling them etc. - perhaps someone more tech-savvy can weigh in on that. As long as you've got your wallet backed up, you shouldn't have any issues though I'd imagine!