To resolve this error kindly follow the below-mentioned steps:
- Login to your VPS via RDP.
- Go to Start → Administrative Tools → Internet Information Services (IIS) Manager.
- Expand your VPS hostname → select the Application Pools option.
- You need to set the .Net Framework version to 4.0 (Integrated) from 2.0 (Classic). Also mark the checkbox 'Start the application pool immediately' and click on OK.
- This will resolve the error of SmarterMail, and will make the SmarterMail functioning as usual.