Can you identify these frequent grammatical errors?

1. Canadians feel they are a leading country in humanitarian aid.
2. When I reached the office, I discovered that I forgot my cell phone.
3. In reference to your letter dated January 6, 2001.
4. Who do you want this memo sent to?
5. My associate really appreciates me helping him.
6. Please call my secretary or myself by Friday.
7. All regional managers reports are due today.
8. People usually get this answer wrong, irregardless of their grammar skills.
9. If you make less than two mistakes on this test, you’re doing well.
10. A group of employees are coming in to see you now.
11. Are these James file folders?
12. Anyone interested in improving their writing skills should take this course