I really cannot say. The web.config says v 13, the app says it is referencing v 12. So, you have two choices:
1) Look at your project references and change them from v 12 to v 13
2) Modify the web.config - change the v to 1 12. Now, there is another weird thing happening here. I believe that assembly version 12.0.1100 was for frm 1.x and v. 12.0.2000.0 was for frm 2.x (and I think frm 3). And the error reports v. 12.1.2000.0 - no clue what is happening there.
Given the above, I'd go with option (1). If that does not help, search the whole project for references to v 12.
- Ludek