Try this.

Open the profile folder:

- TB menu > Help > Troubleshooting Information

- under the Application Basics section next to Profile Folder, click 'Open Folder'

- close TB

- press ctrl-shift-esc (Win) to open the Task Manager

- if there are any TB processes running, R. click > end them

- delete the parent.lock file in the profile folder

- restart TB

- see if the saved file opens

Ed,

Thank you for the step-by-step guidance. Unfortunately, this did not solve my issue. A couple of notes: When using Task Manager, there were no residual Thunderbird processes running. I purged the parent.lock file without issue. When attempting to open an old saved message, and an active instance of Thunderbird is on my system, I receive the same error as noted above. When attempting to open an old saved message and there are no active Thunderbird instances running, I receive a different message (attached).

Hi, I am having the same issue too. 143.0.1, cannot open any saved EML files. Getting both of the pictured messages when trying. Any solutions yet?

Ed, Thank you for the step-by-step guidance. Unfortunately, this did not solve my issue. A couple of notes: When using Task Manager, there were no residual Thunderbird processes running. I purged the parent.lock file without issue. When attempting to open an old saved message, and an active instance of Thunderbird is on my system, I receive the same error as noted above. When attempting to open an old saved message and there are no active Thunderbird instances running, I receive a different message (attached).

Close TB and open the Profile manager. Select the profile you want to use by default > check 'Use the selected profile...' > click 'Start Thunderbird'.

Also make sure TB menu > Settings > General > System Integration > 'Always check to see...' is enabled and click the 'Check Now' button.

kanas said

Ed, Thank you for the step-by-step guidance. Unfortunately, this did not solve my issue. A couple of notes: When using Task Manager, there were no residual Thunderbird processes running. I purged the parent.lock file without issue. When attempting to open an old saved message, and an active instance of Thunderbird is on my system, I receive the same error as noted above. When attempting to open an old saved message and there are no active Thunderbird instances running, I receive a different message (attached).

Close TB and open the Profile manager. Select the profile you want to use by default > check 'Use the selected profile...' > click 'Start Thunderbird'.

Also make sure TB menu > Settings > General > System Integration > 'Always check to see...' is enabled and click the 'Check Now' button.

This method worked for me, hopefully it fixes for OP too. Thanks!