I try to connect RepRapDiscount Smart Controller to Prusa i3 with new ribbon cable 4 ft long. But I have some problems about SD card reader.

Sometime The LCD show"Card inserted" but when enter to menu it show"No SD card"
Sometime when enter in"Print from SD" it show only "Main" (SD card have gcode file) or some weird letters.

How to fix it? Is ribbon cable too long?

ps. Before I change to this wire It work like a charm.

It's most likely too long.

The SD card lines are by far the ones most likely to be affected by length. Your options:

1. Use a cable where each wire is individually shielded from the rest. Unless you can get the cable cheap, this won't be a very cheap option, and even then 4 foot might be way too long. You would also need to put the appropriate connectors on this cable which may prove difficult as such a cable won't be standard IDC ribbon cable.

2. Shorten the cable.

Note: I suspect that the max length will be under a foot.