In lesson 2, section "gismu as sumti":
...you don't need cu after mi (I/me/we), do (you, the person(s) I'm talking to) or any words like this ('pro-sumti', in Lojban jargon).
In lesson 3, section "Questions":
...mi cu na nelci la bil. means "It is not true that I like Bill," or in other words, "I don't like Bill."
Tip: By default, na is followed by a selbri. Since cu has the job of indicating that a selbri is coming up, na makes it superfluous. So you can simply say mi na nelci la bil.
The use of cu after mi in the second paste is not explained, and to say that it is not needed because the na is there is to say that it would be needed if na were not there.
In lesson 4, section "Numbers and articles":
lu'o le and lu'o lo are very useful concepts, even without explicit numbers, and there are shorter ways of saying each when no number comes between them: lei and loi respectively. So the three men carrying the piano could be expressed as loi nanmu cu bevri le pipno, and the throng of women kissing me (!) as lei pano ninmu cu cinba mi.
The last bridi, "lei pano ninmu cu cinba mi." should not contain pano.
In lesson 5, section "Answers to Exercises":
Exercise 1, question 4: a quarter to twelve
Given answer: li papa pi'e ni'u pamu or li pare pi'e vomu.
This is incorrect. It should be {li pare pi'e ni'u pamu} or {li papa pi'e vomu}.
In lesson 6, section "Time with sumti":
la jan. cliva le barja ti'u la jaucac. .i la la suzyn. klama le barja ti'u la feicac.
1) s/jaucac/daucac/
2) s/la la/la/