Autoexposure error on my nikon d5100?

Its appears in all modes autoexposure error except M mode and when i open the flash to use the same message appears, any answer?

It would really help if you told us what the error message was. Likewise, we'd be better prepared to help if we know the lens used and what other settings (such as ISO) you're using and the lighting situations.

To answer this question would be like answering, "There's something wrong with my car" and not being given any details.

On the screen it reads "auto exposure error?" or something else. Have you noticed over or under exposed photos?

Be sure first all the connections between camera and lens are clean and making connection. Also try a different lens and see if you get the same result.

If I get you correctly the message doesn't appear in full manual, is that correct? That would make sense since you're in control of exposure at that time. And, if I understand, when you pop the flash it seems to expose correctly?

If the camera isn't exposing correctly and you know the lens is on correctly and working then perhaps a call to Nikon is in order.

Is your exposure compensation set to zero?

Perhaps this video tutorial will help you:
http://www.nikondigitutor.com/eng/d5100/index.html Who better than Nikon to help you learn to use your Nikon D5100?

Of course, actually reading and studying the Owner's Manual for your camera also helps.

Check that EV (lightmeter) is at 0.