I just skimmed the
DLink DP-G310 emulator, and it appears this print server only supports WEP, which suggests it’s quite old. I do see it went through several revisions, and was discontinued in Oct 2007. So I suppose later revisions might have supported better security.
Anyway, I’m only mentioning it because a lot of this networking equipment, particularly consumer grade devices, are made VERY cheaply, and will just reach their limit after 5-6 years. I'm not saying this is definitely the case, but when something this old has been working perfectly for years, then suddenly starts getting flakey, I start to wonder if it's just not the normal life cycle reaching its end.
So what the history of this device? What’s the revision? Is this only a recent problem? Did you introduce other changes (e.g., new wireless router)?