I think it's absolutely fine to remind that running the site is costly and donations are welcome.
It's just about the frequency and the style "Oops, problems. Read this or you can't do shit" feels like grabbing someone by the neck and spewing: "Listen here, you little shit..." in his face.
Oops! We ran into some problems.
I've been using internet forums for 30 years and have seen maybe a dozen forced threads over this time. This is disturbing and looks amateurish. Make a banner, make the bell go red, send a private message to everyone - anything.
/rant