Logging into one of my websites as a host user i'm getting the bane of my existence error message: A Critical Error has Occurred.

In reviewing my log files i have the following:

2017-11-12 15:51:14,027 [WEB1][Thread:7][ERROR] DotNetNuke.Services.Exceptions.Exceptions - ~/Default.aspx?tabid=41&error=An unexpected error has occurred

System.NullReferenceException: Object reference not set to an instance of an object.

at DotNetNuke.Modules.Admin.Authentication.DNN.Login.OnLoginClick(Object sender, EventArgs e)

at System.Web.UI.WebControls.LinkButton.OnClick(EventArgs e)

at System.Web.UI.WebControls.LinkButton.RaisePostBackEvent(String eventArgument)

at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

2017-11-12 15:51:28,949 [WEB1][Thread:46][FATAL] DotNetNuke.Framework.PageBase - An error has occurred while loading page.

System.NullReferenceException: Object reference not set to an instance of an object.

at DotNetNuke.Modules.Admin.Authentication.DNN.Login.OnLoginClick(Object sender, EventArgs e)

at System.Web.UI.WebControls.LinkButton.OnClick(EventArgs e)

at System.Web.UI.WebControls.LinkButton.RaisePostBackEvent(String eventArgument)

at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

2017-11-12 15:51:28,949 [WEB1][Thread:46][ERROR] DotNetNuke.Services.Exceptions.Exceptions - ~/Default.aspx?tabid=41&error=An unexpected error has occurred

System.NullReferenceException: Object reference not set to an instance of an object.

at DotNetNuke.Modules.Admin.Authentication.DNN.Login.OnLoginClick(Object sender, EventArgs e)

at System.Web.UI.WebControls.LinkButton.OnClick(EventArgs e)

at System.Web.UI.WebControls.LinkButton.RaisePostBackEvent(String eventArgument)

at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

If anyone has experienced this error and has found a solution your advice is appreciated. To my knowledge nothing on this server for this particular site has been changed. Logging in returns that error and I cannot see the administrators toolbar so it's troublesome to interact with the site apart from using SQL directly.