I sent a bug report to HEC. Meanwhile, i kept messing around with the project, and it begun working! I updated my email to HEC with the new information, see it below
“Regarding my yesterday’s bug report, I have some additional information. I was using a 3 h computation interval, a bit large considering the distance between river stations, but it is a very slow river, and also a preliminary simulation. I decided to change the time interval to 1 hour, and, presto! the error message disappeared, and everything seems to be working fine.
Even if a 3 h time interval were grossly wrong, symptoms would quite different, instabilities or so, not a “missing initial condition“.
Any ideas?