CRM 2011 - Error Importing Solution

When trying to Import an unmanaged or managed solution, you may experience the following error:

Error while Importing a solution in CRM 2011 – The solution file is invalid. The compressed file must contain the following files at its root: solution.xml, customizations.xml, and [Content_Types].xml

Issue

The issue can be either one of a few, could be that the file  is corrupt, the file has been tampered with, but the most probable cause is that the file has been zipped/compressed incorrectly. 

You should check that there are 3 .xml files in the root of the solutions .zip file, which should include:

• solutions.xml
• customizations.xml
• [Content_Types].xml

Resolution

The obvious thing would be to try exporting the solution again and try importing this, however if this is not an option, please do the follow:

1. Extract the solution .zip and navigate to the folder until you can see the 3 .xml files, along with the other contents of the solution.

2. Select all files and folders, then right click and use the Send to > Compressed Folder option as displayed below:

Now try importing the newly created .zip solutions file, and you should be fine.