how to convert string quarterly dates into numerical values?

I have a column vector with quarterly dates ('Q1-2011', 'Q2-2011', etc.). I need to convert all entries in this column vector into strings so that I can create a time-series plot. Any ideas how to do it? I tried this program:

DateString = DataRussiaFinal1114(:,1); 
    formatIn = 'QQ-YY';
    dates = datenum(DateString,formatIn);

But datenum gives an error: The input to DATENUM was not an array of strings.

[dpb]

What does

whos DateString

return? Either

>> datenum(['Q1-2011'; 'Q2-2011'],'QQ-YY')
ans =
    734504
    734594

or

>> datenum({'Q1-2011'; 'Q2-2011'},'QQ-YY')
ans =
    734504
    734594
>>

as character array or cellstr array work so must be some other storage issue that we can't see by description only...must see actual data.