Hello, anirudhad. 

All QuickBooks Desktop software enables you to set up different users to access a company file. However, if you're using a single license (standard), accessing and making changes on the file can only be done one at a time. You can get an error upon logging-in to QuickBooks when:

• The accountant or user logging into the company file is using Remote Access and did not log out from a previous session.
• The user is already logged into the company file from a different workstation.
• An electrical problem caused an issue in the network.

For more details, please visit this link: Set up a multi-user network for QuickBooks Desktop. 

You might also consider reading this handy article that will discuss you more about access limits in single or multi-user mode: Tasks that can be performed in a single or multi-user mode in QuickBooks Desktop.

I'm always here if you need more help with logging in to the account. Keep safe and enjoy the rest of the day!