I think it's prudent to always use the latest version of the platform.
For the same reason I believe old versions may not be easily (if at all) accessible.
If the stated "Server error 900" persist, send an issue report to [email protected] Provided information should include: device specifications, OS version, trading account username, screenshots, issue description.
I'm sorry to hear that you're having problems with your computer. Conditions you give server error = 900 error, which basically means that the lack of resources on the computer to handle file sharing over the network.