How do I get data on multiple securities using history function from Bloomberg?

I am using the following code:

c = blp;
s = ['TY1 Comdty';'TU1 Comdty'];
s = cellstr(s);
f = 'px_last';
startdate = datenum('01/01/1990');
enddate = now;
d = history(c,s,f,startdate,enddate);

and this is the error I get:

------------

Attempted to access j(1); index out of bounds because numel(j)=0.

Error in blp/history>eventHandler (line 418)
  outInd(i) = j(1);

Error in blp/history (line 245)
[d,sec] = eventHandler(b,s,f);

Error in backtest (line 9)
d = history(c,s,f,startdate,enddate);

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Can anyone help me out?

[dpb]

>> help history
history not found.

What're history and blp?

Can you retrieve any data to start with before moving to more?