Hi Michael,
I’ve checked it - it is self.dict[‘text’] = unicode (text) in line 274, exactly the same line as in Python libraries on a PC, on which the same program is running.
I’m really confused now what to do, because I can’t swap these two PCs over, due to other people in the Lab who already set up their experiments on this stim PC in the EEG booth.
Also, I don’t think that anyone would have changed anything in Python libraries. And it does look like the line is the same as it should be.
As it doesn’t look promising to solve this soon, I should probably give up with Psychopy and switch to another program we have in the Lab 
It’s a pity because I do like the builder.
Thank you anyway for your responses!
Alena