Please follow the below provided solutions one-by-one In order and check to see the issue resolved.
Solution1. Do IISRESET on SharePoint Servers
Solution2. Restart all the SharePoint Servers
Solution3. Enable anonymous authentication for the website in IIS.
Solution4. Restart the SharePoint Search Host Controller in services.msc
Solution5. Issue with the permission of user, could be The user doesn't have access to the site, but has access to the library.
If still the issue is not resolved by the above steps. Please do the below.
A. Open IIS Manager on SharePoint server and do the following steps:
a. Right Click on “Web Application” where you are getting error.
b. Explore the Web Application.
c. Open Web.config file.
c. Search for serviceHostingEnvironment under system.serviceModel
d. modify the entry as follows:
.
e. Save the Web.config
f. Reset IIS.
- See more at: http://expertsharepoint.blogspot.in/2014/07/the-server-was-unable-to-save-form-at.html#sthash.a7QLBqW7.dpuf