I tried to calculate, with NDSolve, numerically the velocity field of the two-dimensional jet; that is, fluid flowing from a hole (actually a slot) in a wall into a patch of fluid initially at rest. Originally, I wanted to post here the notebook; but it came out als FullForm, so it was rather long and (I think) difficult to read. So I attached it. After starting the program, I got several messages; a final one reads:

NDSolveValue::nlnum: The function value {<<1>>} is not a list of numbers with dimensions {675} at {t,p[x,y,t],u[x,y,t],v[x,y,t],(p^(0,0,1))[x,y,t],(u^(0,0,1))[x,y,t],(v^(0,0,1))[x,y,t]} = {0.0001,<<5>>,{{0.,0.,0.,0.,0.,0.,0.,0.,0.,0.,0.,0.,0.,0.,0.},{0.,0.,0.,0.,0.,0.,0.,0.,0.,0.,0.,0.,0.,0.,0.},<<12>>,{0.,0.,0.,0.,0.,0.,0.,0.,0.,0.,0.,0.,0.,0.,0.}}}. >>

Apparently, the error reported with this message prohibited the program from running.

I do not understand the message. Can anybody tell me what type of error possibly happened in the program, and what is to be done to avoid it ? Is it possible to analyze the NDSolve process so that one can explitcitly arrive at the point where the error occurs ?