• Error changing modules.
• Error switching modules.
• An error occurred when attempting to change modules.

Solutions

Try the following solutions, in order. After performing each solution, test to see if the issue recurs.

Solution 1: Install the current Lightroom update.

In Lightroom, choose Help > Check For Updates.

Solution 2: Re-create the preference file.

Drag the preference file to the Trash (macOS) or Recycling Bin (Windows) and then restart Lightroom. For preference file locations, see:

• Preference file and other file locations | Lightroom and Lightroom 6
  
• Preference file and other file locations | Lightroom 5
• Preference file and other file locations | Lightroom 4
• Preference file and other file locations | Lightroom 3.x
• Preference file and other file locations | Lightroom 2.x
• Preference file and other file locations | Lightroom 1.x

Solution 3: Reinstall Lightroom

Uninstall and then install Lightroom again. 

For Lightroom, see: 

• Uninstall or remove Creative Cloud apps
• Download your Creative Cloud apps
  

• Uninstall Lightroom manually

Solution 4: Create a different catalog.

To determine whether the problem lies with the catalog you’re using, import some images into a new catalog and then restart Lightroom.

Solution 5: (Lightroom 3) Uninstall Nik Software plug-ins.

Uninstall any Nik Software plug-ins you have installed, including Photoshop plug-ins, and then restart Lightroom. If Lightroom starts, make sure that you're using the most recent version of the Nik plug-ins. For help uninstalling Nik plug-ins, visit Nik Software Support.

Solution 6: Set correct permissions on Lightroom folder inside Application Support.

Note: Use this solution if you are asked for your serial number after you relaunch Lightroom after getting this error.

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 you 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.

Important: (macOS) Apple made the user library folder hidden by default with the release of OS X 10.7. If you need access to files in the hidden library folder to perform Adobe-related troubleshooting, see How to access hidden user library files.

Solution 7: Try a different user account.

Copy the Lightroom folder into a new user account or other existing account on your computer. Then, restart Lightroom. The Lightroom folder is in the following locations:

• Windows: [user name]\AppData\Roaming\Adobe\
• macOS: [user name]/Library/Application Support/Adobe/

Important: (macOS) Apple made the user library folder hidden by default with the release of OS X 10.7. If you need access to files in the hidden library folder to perform Adobe-related troubleshooting, see How to access hidden user library files.

Additional information

Adobe is researching this issue.