New Registration... Help!

Please can someone help me? I'm a pianist, but I'm very low 'tech' unfortunately, so am not good with installing new softwares on my computer! I have a Mac (10.6.8) and today I bought the 'Pianoteq 4 Stage' software. I paid for it, received the purchase confirmation, then attempted to download the latest version (4.2.0).

The latest version will duly download me a DMG file. But when I try to open this to complete the installation process, a window pops up and says the following: "The following disk images couldn't be opened... Image: pianoteq_state_setup_ ... Reason: invalid checksum"

Have tried it several times, to no avail. So I then looked around on the Pianoteq site, and it told me that, should the latest version fail, you can download the previous version (which I think is 3.6.8). I have done this successfully.

The problem is the older version is nothing like as good. Doesn't have the same instruments (particularly the one I want - the Bluethner Chamber thing) and doesn't have access to the same settings/amends.

I have obviously sent an email to the support team just now, and will wait for a reply. But in the meantime, I wanted to ask here, does anyone know how I can rectify this so that I may use the newer version?

Hopefully my question is clear - apologies if I left anything important out.

p.s. if anyone is kind enough to reply, please please please can I request that you keep the tech jargon at a minimum, because I really won't have a clue what you mean otherwise. Assume I know nothing!

Thanks again everyone.

Will