I would suggest you not to panic at this point, please follow the steps I have followed to resolve this error.
Usually this happen because of windows or SharePoint update interruption while installing the patches on your SharePoint server.
Derived method 'Requires WebPartClientScript' in type 'Microsoft.SharePoint.Taxonomy.TermProperty' from assembly 'Microsoft.SharePoint.Taxonomy version=15.0.0.0, Culture=neutral, PublickKeyToken=71e9bcs111e9429c' cannot reduce access
As usual I have checked the below points,
- In IIS Manager, all application pools and sites are up and running
- On Service console, I have checked the SharePoint and SQL related services are up and running.
In my case all of the stopped and stuck.
To resolve this problem, I tried to ran the SharePoint Configuration Wizard , exactly on second step , It failed and given me the suggestion to look into the log file.
Honestly , I did not get anything from the log file to narrow down this problem.
But I recollect my previous activities on this server , Late night I was trying to update the Windows 2008 R2 SP through windows updates and it failed.
Now I have checked the Installed updates for the SharePoint 2013 on Control Panel\Programs\Programs and Features and then click the link "View Installed Updates" on the right hand side.
It shows all my SharePoint related upgrades are failed.
Now I clicked the each individual item and it gives the me the Knowledge Base with code and downloadable link. This time I have ensured all the updates are installed on my server.
This time,My server started to working correctly.