Common problem with March 2018 security fixes for SharePoint 2013 – AccessKey too long, cannot be more than one character

We received reports from several customers about a problem in the March 2018 security fixes for SharePoint 2013. The full server packages of March 2018 CU are not affected by the problem.

Performing actions in the User Profile Service Application like clicking on Configure Synchronization Settings or Start Profile Synchronization returns an error page and the following error in the ULS logs:

Application error when access /_layouts/15/ProfileSynchronizationServiceProvisionPage.aspx, Error=AccessKey too long, cannot be more than one character. Parameter name: value
 at System.Web.UI.WebControls.WebControl.set_AccessKey(String value)
 at Microsoft.SharePoint.Portal.WebControls.InputFormButtonAtBottom.set_AccessKeyLocId(LocStringId value)
 at ASP._layouts_15_profilesynchronizationserviceprovisionpage_aspx.__BuildControl__control11()
 at ASP._layouts_15_profilesynchronizationserviceprovisionpage_aspx.__BuildControlProfileSyncProvisionSettingsForm()
 at ASP._layouts_15_profilesynchronizationserviceprovisionpage_aspx.__BuildControl__control4(Control __ctrl)
 at System.Web.UI.MasterPage.InstantiateInContentPlaceHolder(Control contentPlaceHolder, ITemplate template)
 at ASP._admin_admin_master.__BuildControlDeltaPlaceHolderMain()
 at ASP._admin_admin_master.__BuildControl__control27()
 at ASP._admin_admin_master.__BuildControlSPHtmlTag()
 at ASP._admin_admin_master.__BuildControlTree(_admin_admin_master __ctrl)
 at System.Web.UI.MasterPage.CreateMaster(TemplateControl owner, HttpContext context, VirtualPath masterPageFile, IDictionary contentTemplateCollection)
 at System.Web.UI.Page.ApplyMasterPage()
 at System.Web.UI.Page.PerformPreInit()
 at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

We are currently investigating the root cause for the issue.

Installing March 2018 CU on the affected servers resolves the problem.