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How do i deal with this problem?
PhotosynthInstall_21103171042.exe is not a valid win32 application
How large is the file in kilobytes on your hard drive? You might be getting this error because the entire installer file did not finish downloading.
After reading your message I downloaded the installer fresh from the site and installed it on a computer in my house that didn't have the synther installed yet. It installed perfectly for me, so it seems like the file on the website is still good.
When I right click on the installer file and click 'Properties', it says that the file size is 10.9 megabytes or 11,488,096 kilobytes. If you right click on the installer and see a number smaller than what I reported, I would suggest that you try to re-download the installer.
Here are two links for the official installer (Right click on either one of these and 'save target as'):
Let me know if you still have trouble.