A problem is presented when the substitution of the numerical values for this function
Uz = (-(1/4) - I/4) (2 Sqrt[\[Pi]])/k 1/Sqrt[k R] E^(-((2 I a n \[Pi])/\[CapitalLambda]) - (n^2 \[Pi]^2)/( b^2 \[CapitalLambda]^2) - (I (k^2 R^2 + (n \[Pi] + k z)^2))/(2 k R)) (Erfi[((1/2 + I/2) (n \[Pi] + k (-R + z)))/Sqrt[k R]] - Erfi[((1/2 + I/2) (n \[Pi] + k (R + z)))/Sqrt[k R]] +
Erfi[((1/2 + I/2) (k R - Sqrt[D^2 k^2 + (n \[Pi] + k z)^2]))/Sqrt[k R]] + Erfi[((1/2 + I/2) (k R + Sqrt[D^2 k^2 + (n \[Pi] + k z)^2]))/Sqrt[k R]])
I used
valplot = { k R -> 1, z -> 1, b -> 1, z -> 0, \[CapitalLambda] -> 1 }
Ux1 = Uz /. valplot
Please, observe that I have a variable kR and sqrt of kR. It is possible to evaluate with a unique value? It is possible to do the parameter independently. Another detail is when a product of parameters is presented. How can it is possible to fix it, this point is important for future plot analysis.