Unable to save site as template + unexpected error has occurred

Problem description:-

User has raised the problem ticket by mentioning “facing problem while saving the site as template”, additionally the templates are getting saved in the solution gallery but not able to activate it also.

Error message:-

An unexpected error has occurred.

Troubleshoot issues with Microsoft SharePoint Foundation.

Correlation ID: acd95f50-4049-4625-9682-aa93aded118f

Troubleshooting done:-

Further debugging in the SP ULS logs and we found some strange facts which are based on event receivers- please refer below-

SPSolutionExporter: Microsoft.SharePoint.SPException: Feature definition with Id 77658379-50ff-4e1e-a431-5652bee07a87 failed validation

Looking for 'ReceiverAssembly' attribute in manifest root node for solution

Looking for 'ReceiverClass' attribute in manifest root node for solution

The 'Format' attribute is invalid - The value 'CheckBoxes' is invalid according to its datatype

I debug further to find out where the problem is-

I downloaded the saved wsp's from  /_catalogs/solutions/Forms/AllItems.aspx to my desktop

Renamed it to .cab

Extracted all the contents and found some interesting facts along with manifest.xml file like-

1.      List Instances

2.      Modules

3.      Property bags

4.      web template

Inside List Instances, I found ElementsFields.xml

Once i opened the above xml file, search for the checkboxes and found the following-

Further exploration on this, it seems that the checkbox attribute is invalid and needs to be modified.

Resolution:-

After this one, the solution is pretty much simple, just go ahead and remove that affected column / remove the affected content type – does not require IISRESET also.