introducing "safe" DLL causes internal compiler error

i'm using a third-party DLL that's been suited to work around WP8 and Unity not referencing the same DLLs, but in my case Unity ran into this:

Internal compiler error. See the console log for more information. output was: Unhandled Exception: System.IO.FileNotFoundException: Could not load file or assembly 'System.Runtime, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies.

File name: 'System.Runtime, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'

at (wrapper managed-to-native) System.Reflection.Assembly:InternalGetType (System.Reflection.Module,string,bool,bool)

at System.Reflection.Assembly.GetType (System.String name, Boolean throwOnError, Boolean ignoreCase) [0x00000] in :0

at System.Reflection.Assembly.GetType (System.String name) [0x00000] in :0

at Mono.CSharp.RootNamespace.GetTypeInAssembly (System.Reflection.Assembly assembly, System.String name) [0x00000] in :0

at Mono.CSharp.RootNamespace.LookupTypeReflection (Mono.CSharp.CompilerContext ctx, System.String name, Location loc, Boolean must_be_unique) [0x00000] in :0

at Mono.CSharp.GlobalRootNamespace.LookupTypeReflection (Mono.CSharp.CompilerContext ctx, System.String name, Location loc, Boolean must_be_unique) [0x00000] in :0

at Mono.CSharp.Namespace.LookupType (Mono.CSharp.CompilerContext ctx, System.String name, Location loc) [0x00000] in :0

at Mono.CSharp.Namespace.Lookup (Mono.CSharp.CompilerContext ctx, System.String name, Location loc) [0x00000] in :0

at Mono.CSharp.NamespaceEntry.Lookup (System.String name, Location loc, Boolean ignore_cs0104) [0x00000] in :0

at Mono.CSharp.NamespaceEntry.LookupNamespaceOrType (System.String name, Location loc, Boolean ignore_cs0104) [0x00000] in :0

at Mono.CSharp.DeclSpace.LookupNamespaceOrType (System.String name, Location loc, Boolean ignore_cs0104) [0x00000] in :0

at Mono.CSharp.TypeContainer+BaseContext.LookupNamespaceOrType (System.String name, Location loc, Boolean ignore_cs0104) [0x00000] in :0

at Mono.CSharp.SimpleName.ResolveAsTypeStep (IMemberContext ec, Boolean silent) [0x00000] in :0

at Mono.CSharp.Expression.ResolveAsBaseTerminal (IMemberContext ec, Boolean silent) [0x00000] in :0

at Mono.CSharp.TypeContainer.ResolveBaseTypes (Mono.CSharp.TypeExpr& base_class) [0x00000] in :0

at Mono.CSharp.Class.ResolveBaseTypes (Mono.CSharp.TypeExpr& base_class) [0x00000] in :0

at Mono.CSharp.TypeContainer.DefineBaseTypes () [0x00000] in :0

at Mono.CSharp.TypeContainer.DefineType () [0x00000] in :0

at Mono.CSharp.RootContext.ResolveTree () [0x00000] in :0

at Mono.CSharp.Driver.Compile () [0x00000] in :0

at Mono.CSharp.Driver.Main (System.String[] args) [0x00000] in :0

i've been advised on the plugin's forum that it was a Unity issue. any help?