I came across an interesting issue recently where a customer was backing up a site collection via SharePoint Management shell & the backup process was abnormally terminated. This resulted in the Site being in Read only mode & the following message would show up when users browsed to the site.
“We apologize for any inconvenience, but we’ve made the site read only while we’re making some improvements."
Go to "Site collection Quota & locks" in Central Admin & here is how the Status looks like. It is locked as “Read only" & all settings are grayed out.
Here is more on this behavior & how to get out of this situation.
In SharePoint 2013, we introduced a property MaintenanceMode for Spsite object which indicates the site is undergoing a Maintenance & is read only. SPSite.MaintenanceMode flag can be set on a site for several reasons like content database is in read only state, or site collection is being upgraded, backed up or moved.
If a site gets into a state where the action that set this has terminated in a way where this is still set, we run into this situation.
The way to clear this flag is use the ClearMaintenanceMode method in SpSiteAdministration object. Here is how it can be done via SharePoint Management Shell
# $Admin = new-object Microsoft.SharePoint.Administration.SPSiteAdministration(‘http://weburl/sites/sitecollectionurl’)
The SpsiteAdministration.ClearMaintenanceMode method was introduced in April 2013 CU for SharePoint 2013. So you would need to upgrade the environment to March 2013 & April 2013 update available at Update Center for SharePoint 2013