Download and Instal CS5.5 Trial

I'm trying to download and install the CS5.5 trial on my MacBook Pro.  During the "Extracting" phase in the download assistant, a window pops up with a message saying:

"The following disk images couldn't be opened"

Image: MasterCollection_CS5_5_LS1.dmg

Reason: invalid checksum

What does this mean and how can I resolve this?

I included an image, hopefully to get a better idea of what I am seeing.