Thanks for the reply, but it came too late.
Yesterday I tried using Advance mode and did the same think like in Standard mode where ImgBurn got stuck, but it worked fine. Only think is that the procedure in there is similar like using "Browse for files" icon in Standard mode and that always worked when I opened ImgBurn after it hung and did not want to restart computer.
Today I tried your suggestion to clear MRU files after I got ImgBurn stuck by closing it with selected files, just before burn and it looks like it started to work again. That means I cold use "Browse for folder" icon after reopening and clearing MRU file before clicking on that icon.
One thing I noticed using Advance mode is that the windows change much faster within ImgBurn, than in Standard mode.