SendGrid package throw error on assembly.GetTypes() method

[LOKCHAU8]

I have downloaded the SendGrid package & tested on my sample test program using the Web API method with C#.
The email work fine. But When I integrate it into my production project, My project load up & it check all the
Assemblies load & the appropriate actions.

Here is my C# ccode:-
public static IEnumerable GetAllTypesImplementingType(
Type implementingType,
Assembly[] assemblies)
{
return (from assembly in assemblies
from type in assembly.GetTypes()
where (implementingType.IsAssignableFrom(type)) && (implementingType != type)
select type).ToList();
}

I have 167 dll in my project, none fail on the assembly.GetTypes() method.
Why SendGrid.dll throw an error.