Well, my pupils have great difficulty with the Present Tense & Present Progressive (Continuous), together with the Time Expressions. Their mother language is Hebrew, and Hebrew doesn't differentiate between the two tenses.
It's usual to hear them saying "She is walk" or "She walking", or using the wrong Time Expression, like in "She walks at this moment".
Another common difficulty is understanding the pronoun "it". They don't differentiate between "it" and "they" most of the time. If asked to fill in the right pronoun, like in "Our classroom", many use "we" as an answer. And consequently, there will be mistakes with the Present Tense as well.