An Exception Occurred While Executing a Transact-Sql Statement or Batch

I got this error message while trying to attach DB, if it's your case, go to to the folder where your DB is:

• Right click => properties => security => advanced
• Make sure the correct user has 'full control' permission
• If not:
  • Click on 'Change permissions'
  • Set 'full control' permission to the relevant user (or all of them)
• Try to attach again

It works for me.

Thanks to everyone who tried to answer the question, but I was able to solve it. It is the same procedure mentioned in SQL Server 2008 R2 Express permissions -- cannot create database or modify users. However, in step 6 instead of adding "-m" to an existing parameter, you have to create a new parameter called "-m" and follow the remaining steps. This resolved the issue.

I got same issue but when i tried with query it was succeeded. try below

CREATE DATABASE databasename;

I fixed it a different way
I put the .bak file in "C:\Program Files\Microsoft SQL Server\MSSQL15.MSSQLSERVER\MSSQL\Backup"