Please check this below link and follow the instructions -
If this link does not work check your hosts file and make sure there is no adobe entry.
Windows location for hosts file - C:\Windows\System32\drivers\etc
Mac Location for hosts file - How to Edit the Hosts File on Mac OS X - TekRevue
Set correct permissions on Lightroom folder inside Application Support
The Lightroom folder inside Application Support could have the wrong permissions preventing Lightroom from writing to it, which can cause this error.
- Navigate to the following folder: /Users/[user name]/Library/Application Support/Adobe/Lightroom.
- Highlight the Lightroom folder and chose File > Get Information.
- Under Sharing & Permission, verify that your have Read & Write Privileges. If not, click the padlock icon at the lower right, enter your password when prompted, then click the Read only entry and select Read & Write.
For more information refer to : Error changing modules
Please let us know if it helps.
Thanks for trying to help! However, I checked and I already had read and write privileges.
When I opened Lightroom again, it said that it could not create the required folders for filter presets and keyword sets. So maybe that's why I can't use it. Do you know how to fix this?
Please try these below mentioned steps
Step 1: Uninstall and reinstall LR
Step 2: If above step does not work, create a new user account on your computer (Make sure it is admin)
Windows - Create a user account - Windows Help
Step 3: Install Lightroom in that new account
Step 4: Switch back into your own account and then launch/open Lightroom and it should work fine
Step 5: Once done then you can get rid of the new account that was created.
Victoria, would you please share the screen shoot of the error.