White "flash" at the end(or start?) of my movie

Ok, as the title suggests, I have this fairly simple movie that shows a series of random images as they scroll slowly across the page. Then, when the first one has reached the end of the line, the script restarts and should smoothly segway into the next image going across the screen…

However, every time this restarts, a white flash comes, and I can’t for the life of me figure out why.

The script is slightly too large to put as an attachment so just PM me your emailadress and I will send it to you.

TIY,
praxiz