I'm not sure if it is mirc's or euIRCnet's or NNScript's fault, but the network name of euIRCnet is euIRCnet and not euIRC.
Change the name of the euIRCnet server group in the Connect dialoge of mirc by "Edit" to euIRCnet. also, you have to append "net" to the names of the variables %nick.def.euIRC and %nick.away.euIRC (and other euIRCnet entries if necessary) in the Variables section of your aliases.
Now it should work fine and for example variables like &away which use the $network variable do also work.