what are the most common english error students tend to make

[Dr. Jamshid Ibrahim]

Originally Posted by Francois

You guys forgot the damn phrasal verbs, that inextricable maze designed to trip up the poor souls who once dared to learn some English, but whom the Gods cursed to meander purposelessly forever, trudging through the mud of their wordless thoughts, bemoaning their fate, confounded with their own ignorance.
FRC

Your name suggests you are French. Phrasal verbs are Germanic not Romance in origin. Understandably you can't feel comfortable with them. But don't worry English has for every Germanic phrasal verb a corresponding Romance word (uslally long words - multi-syllabic):
give up: abandon
give in: surrender

Common Mistakes should be organised as follows (for the sake of convenience):
1. lexical common mistakes (False Friends, collocations, phrasal verbs, confusing words (economic/economical)....
2. Grammar Mistakes (tenses, number, prepositions, article...)
3. Specific Mistakes: Mistakes depending on learner's culture and language interference
3. Mistakes in Pronunciation and Spelling
3. Register and Style Mistakes (formal/informal English, business register..), Englishes: Be / AmE...

[Omar!]

Originally Posted by Susie Smith

I'd like to add that errors are partially determined by the student's mother tongue since there are so many different language structures.

Yes , I agree that effecting of the mother toungue is common error for most of students .