Inheritance security rules violated by type: Derived types must either match the security accessibility of the base type or be less accessible in asp.net 4

Hello,

We have done framework migration from 3.5 to 4.6.1, since Framework 4 and above uses Level 2 Security Transparent Model we are getting this error, "Inheritance security rules violated by type: Derived types must either match the security accessibility of the base type or be less accessible" in Medium Trust.

We have not declared any Security Attributes in any of the assembly, Is there any way to overcome this problem by using Level 2 Security Transparent Model by making changes in MediumTrust_Web.config and without making any assembly changes ? 

Please help us out, thanks a ton!