hello markus,

yes, i am trying to solve the scattering of cylindrical nanoparticles, or better said in my special case µm particles. i have tried your advise with arbitrary precision number, but still the error arise.

dn[mmm_, j_] := ((BesselJ[mmm - 1, j]/BesselJ[mmm, j]) - mmm /
   j) (*logaritmic deriviate *)

from my nb is the troublemaker.

After changing in

dn[mmm_, j_] := 
 Block[{$MaxExtraPrecision = 1000}, 
  N[((BesselJ[mmm - 1, j]/BesselJ[mmm, j]) - mmm /j), 
   700]] (*logaritmic deriviate *)

the same error showed up.

Fortunatly i solved my problem 2 days ago with a bypass.

thx for your help.

best regards walter