ofxTwitter + other async request -crash


I hope someone has an idea of how to solve this:
I am trying to create a “translator” that translates tweets into pictures using individual letter images from this database: http://www.ualphabets.com/letters.php
So my approach is: first I create a vector that contains the individual letter images for the finnish alphabet (in this case). This works fine and I can also display the alphabet. To do that I’m using an async request and process it further.
After that I want to read the latest tweets that are e.g., tagged with #photography. This also works fine on an individual basis.
What is a problem is displaying the tweets after loading the letters. It’s clearly (I think) not a memory problem of the application. Sometimes it actually works. But more often the app crashes pointing an “Thread1:EXC_BAD_ACCESS”-error in the file OS X 10.9/usr/include/c++/4.2.1/bits/basic_string.h/class basic string in the following line:
size_type find(const basic_string& __str, size_type __pos = 0) const { return this->find(__str.data(), __pos, __str.size()); } (line 1576-1578)

this is the console log:

[notice ] ofxTwitter::urlResponse: async_req loaded ok.
ERROR: searching
[notice ] ofxTwitter::newResponse: Tweets received.
[notice ] ofxTwitter::parseResponse: (1) Tweets ready

how I am sending the ofxTwitter request:

if (tweetCounter==0) {
        ofxTwitterSearch search;
        search.query = "photography";
        search.count = 1;
    // Print tweets:
    int maxLineSize = 90;
    if(twitterClient.getTotalLoadedTweets() > 0) {
        tweet = twitterClient.getTweetByIndex(actualTweet);
        ofDrawBitmapString("Text:", ofPoint(10,300));
        string text = tweet.text;
        for(int i=0;i<(text.length()/maxLineSize)+1;i++) {
            ofDrawBitmapStringHighlight(text.substr(i*maxLineSize,maxLineSize), ofPoint(20,300+(30*i)));

any ideas?

at a quick glance you might want to check text.length() to make sure it is greater than 0