Intentional or not, that is Portuguese for "to make a mistake".

It's also a netspeak spelling of the English word "error." (For some reason it's considered humorous to transform -er and -or into -ar.)

It is? I can safely say I've never seen anyone say "errar", ever.

It's a general thing some people do. Anything that ends in an -er sound can be replaced with -ar for apparent hilarity. I think the most common (and maybe first) example is "winnar," though there are many more.

Nevar, evar?