Can CNG be filled into LNG tanks?

I agree with yankee, they are 2 very different pressures and temperatures. I'd not want to experience the results of a tank made for one and filled with the other. NOTES BELOW from  http://www.ngvc.org/tech_data/index.html

Fuel Storage
Most NGVs operate using compressed
natural gas (CNG) so the fuel takes up less space. CNG is stored on
board vehicles in high-pressure (3,000-3,600 pounds per square inch) in
tube-shaped cylinders that are attached to the rear, top or
undercarriage of the vehicle.  The cylinders meet very rigorous safety
standards. They are made of high-strength materials designed to
withstand impact, puncture and, in the case of fire, their pressure
relief devices (PRDs) provide a controlled venting of the gas rather
than letting the pressure build up in the tank.

Natural
gas may also be stored on-board in the form of liquefied natural gas or
LNG.  To become LNG, natural gas must be cooled to –260 degrees
Fahrenheit.  The biggest advantage of LNG over CNG is space
requirements. LNG requires only 30 percent of the space of CNG to store
the same amount of energy.  In order to keep the LNG cold, LNG is
stored on-board vehicles in thermal storage tanks.  In other words,
sophisticated thermos bottles. 

49 CFR 178.56 – Specification 4AA
welded steel cylinders
CNG cylinders for fueling stations.
Generally not used for new CNG fueling stations. ASME
vessels now generally used.
49 CFR 178.57 – Specification 4L welded insulated cylinders
LNG vehicular fuel tank requirement called out in NFPA 57.
Option is meeting ASME Boiler and Pressure Vessel
Code.

49 CFR 571.304, FMVSS 304 – Compressed Natural Gas Fuel Container
Integrity CNG motor vehicle fuel containers
DOT Federal Motor Vehicle Safety Standard for CNG motor vehicles 

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