Consider the two idealised systems (i) a parallel plate capacitor with large plates with small separation and (ii) a long solenoid of length L >> R, radius of cross-section. In (i) E is ideally treated as a constant between plates and zero outside. In (ii) magnetic field is constant inside the solenoid and zero outside. 

These idealised assumptions, however contradict fundamental laws as below [NCERT Exemplar]

As, Gauss' law states that,  ${\oint }_S\mathbf{E}·d\mathbf{S}=\frac{q}{{\epsilon }_0}$ for electrostatic field. It does not contradicts for electrostatic fields as the electric field lines do not form continuous closed path.

According to Gauss' law in magnetism,  ${\oint }_S\mathbf{B}·d\mathbf{S}=0$

Which means that the number of magnetic field lines entering the Gaussion surface is equal to the number of field lines leaving it.
It contradicts for magnetic field, because there is a magnetic field inside the solenoid and no field outside the solenoid carrying current but the magnetic field lines form the closed paths.