A Warning message in AFT Impulse.

Full message is:

Flow is into system at Reservoir Junction X. Pipe intake elevation above the surface will supply gas, not liquid.

When a pipe exits above a reservoir junction liquid level it is only meaningful if it is discharging into the reservoir. If the pipe becomes an intake, it will not supply liquid, but instead supplies whatever vapor is above the reservoir liquid. This warning alerts you to the fact that the reservoir had a pipe above liquid level. AFT Impulse assumes the intake fluid is the same as the reservoir fluid, but that is likely not the case. Results are probably invalid.