Probability score: 0.8  

Question improvement suggestion: Provide the exact version of Trados Studio 2021 you are using, as well as your operating system version. This will help in diagnosing the issue more accurately.  

In the meantime, based on the information you have provided, here is a suggested answer to your question:  

Hello,  

It seems you're encountering an issue with starting Trados Studio 2021 due to the error message regarding the 'Sdl.TranslationStudio.Api.ProjectManagement.IProjectManagementService'. Here are some steps you can follow to troubleshoot and potentially resolve this issue:

**Step 1:** Close Trados Studio completely.  

**Step 2:** Navigate to the following directory:  

`C:\Users\%username%\App Data\Roaming\SDL\SDL Trados Studio\16`  

If you can't find the path, ensure that hidden items are visible in Windows File Explorer by clicking on the "View" tab and checking the "Hidden items" checkbox.  

**Step 3:** Rename the `Plugins` folder to `Plugins_old`. This will disable any third-party plugins that might be causing the issue.  

**Step 4:** Optionally, you can run a repair installation of Trados Studio. To do this, go to Control Panel > Programs and Features, find Trados Studio, right-click on it, and select "Repair".  

**Step 5:** Restart your computer and then try to open Trados Studio again.  

If the issue persists, you may want to check for any antivirus software that could be interfering with the application. Adding the Trados Studio installation folder as an exception in your antivirus settings can sometimes resolve such issues.  

If none of these steps work, please consider checking for any recent Windows updates or reinstalling Trados Studio as a last resort.  

I hope this answer addressed your question. If not, please reject the answer, add the question improvement suggestion information, and click the RWS Community AI checkbox on the right to try again.  

RWS Community AI