If you encounter the error 'Could not copy obj debug netcoreapp2 to bin debug' while working with .NET Core applications, there are a few potential solutions to try.

1. Clean and Rebuild:

One common solution is to clean the solution and then rebuild it. This can help resolve any dependencies or build issues that may be causing the error.

2. Clear the Bin and Obj Directories:

Sometimes, stale files in the bin and obj directories can cause conflicts. Manually deleting the contents of these directories and then rebuilding the project can help resolve the error.

3. Check File Permissions:

Ensure that the user running the build process has the necessary permissions to read, write, and delete files in the project directories. This can often be a factor in build errors.

4. Update Packages and Dependencies:

If you are using NuGet packages or other dependencies, ensure that they are up to date. Outdated packages can sometimes cause build issues.

5. Check for Long File Paths:

.NET Core has limitations on file path lengths, and having long file paths can cause build errors. Try shortening file paths and reorganizing project directories if necessary.

6. Check for Locked Files:

Ensure that no other processes or applications are locking the files in the project directories. Sometimes, locked files can prevent the build process from completing successfully.

By following these troubleshooting steps, you can often identify and resolve the error 'Could not copy obj debug netcoreapp2 to bin debug' in your .NET Core application. If you continue to encounter the error, consider seeking support from the .NET Core community or the platform you are using for your development environment.