" the plotting stops at the sixth security"
for sec = 'ticker_list'
iterates over the characters of the char array 'ticker_list' (so sec is at first 't', then 'i', etc.). The sixth character is '_'. I assume that 't', 'i', etc. can be matched to a ticker, but not '_'. Of course, none of this is what you want. I suspect your code should be
for sec = ticker_list %iterate over the columns of the cell array instead of characters of a string
%...
d = fetch(c, sec{1}, field, date_begin, date_end);
Note: Learn to use the debugger. Had you used it and stepped through your code as it executed, you would have noticed the problem immediately.
