Question: I deployed a webpart by admin user in Visual Studio 2013 through in SharePoint 2013. 

It's working fine. But when I deploy using another user which already have admin permission then it is showing below error.

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> Error occurred in deployment step 'Retract Solution': Object reference not set to an instance of an object. 
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Answer: 
I had same problem and my solution was related with no space in disk for deployment. ps.: database disk.
I had same problem and i tried whatever was suggested in the blog. Like uninstall solution etc. Then I did a restart of system. And opened a new solution and tired to deploy. 

But this time the error was very clear, I got a message it was due to increase in database size. After reducing deployment worked correctly.