Your first invocation of fread() failed because you had closed the file first, making fid invalid. You seem to have noticed this.
Your second attempt is because of the differences of reading the file versus writing it. In addition, the position of MATLAB within the file. Notice that the following won't work either:
fid = fopen('tst.txt', 'wt');
fprintf(fid, 'Hello there Jonathan');
[~, count] = fread(fid, '*char');
You REALLY don't want to read and write a file at the same time. It's asking for trouble. Yes, you can use the '+' character but unless you are absolutely sure of where you are in a file, it's going to become a nightmare quickly. Instead, you'll want to close the file and then reopen it in READ mode... then run fread().