The misspelling "unles" was discovered by Spell Check. I selected the correction "unless", and selected "Change all". This made Spell check go into an infinite loop inserting the letter "s" at the end of the misspelled word, resulting in something like "unlesssssssssssssssssssssssssssssssssssssssssssss". The loop eventually stopped but I had to kill the TeXnicCenter.
The error seems to be consistent. I run 1 Beta 7.01 - unstable ('Greengrass').