If your assembly is signed by strong name key file you will have problems calling non strong named assemblies. You can bypass this with reflection, but it adds a couple of other issues.
There's another possibility. And that is to sign a non strong named assembly using MSIL.
Here are the steps: 1. Obtain MSIL of the given non signed assembly:
C:\ildasm NonSigned.dll /OUT:MyAsm.il
2. Rename the original assebmly to prevent it from getting overwritten.
3. Rebuild the assembly from IL.
C:\ILASM MyAsm.il /DLL /KEY:MyStrongKey.snk
Credits goes to Jayant D. Kulkarni who posted this in a comment over at CodeProject.