It could be powederd detergents ( if you use them) as they can cause blocks if not fully disolved, but thats not usually a problem if you have a mesh filter in your tank pre pump.
Also machine has'nt be use for some time (or is older) is'nt it hard water near you ? it may be limescale breaking lose so might be a idea to descale it. More information as to age, maker, type and history of machine would be help diagnosie the problem.
If it happens again I find a tooth brush invaluable for unblocking jets and not damaging them.