Not sure if it's what you're seeing but I had the wee fella's running on a 4gb card, all hunky-dory. I borrowed the 4gb (max my new sat-nav would take) & replaced it with an 8gb. DSTT kept freezing with the 8gb one in, wee fella not best pleased. Soon as I replaced the 8gb with the 4gb I'd ordered all's well again.
Hopefully your fix is as simple as that.
HH.