Why is this sentence wrong?
 

A grammar book tells me this sentence is wrong. Does anyone know why? Thanks!

Enviamos mensajes de texto desde hace cincuenta años

Except for the period at the end of the sentence, it seems correct. What is the context?

Maybe llevamos enviado etc....

The only "mensajes de texto" I know are SMS, though the 50-year period is impossible (it's a factual error, not a grammar error)

I agree with ROBINDESBOIS that maybe the book isn't eager to accept the phrase as it is common but sounds the type you'd read in a headline or a sign. You may go:

Enviando mensajes de texto desde hace cincuenta años

that shows better the notion of continuity for a corporative ad, or

Llevamos cincuenta años enviando mensajes de texto

as "that is what we do" (Robin Williams will use a funny voice to add "Help us!")