Please help: AMG error x-momentum
 

I am modelling a pulsatind 3-D air jet using LES, with an inflow velocity given by V=10(1+0.3sin(5t) where t=time. I have written the UDF and it is read ok by fluent. When I try to solve the proble i get an error of "divergence detected in AMG solver: x-momentum"

Has anyone got any idea what that error might be?

I will appreciate your help. Thank you. George.