it seems to come down the this. This entry in the module section <add name="UploadHttpModule" type="Brettle.Web.NeatUpload.UploadHttpModule, Brettle.Web.NeatUpload" preCondition="managedHandler" /> is the cause
if commented out can log in if not commented no login.
<modules runAllManagedModulesForAllRequests="false">
<add name="UploadHttpModule" type="Brettle.Web.NeatUpload.UploadHttpModule, Brettle.Web.NeatUpload" preCondition="managedHandler" />
<add name="ScriptModule" type="System.Web.Handlers.ScriptModule, System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" preCondition="managedHandler" />
<add name="Compression" type="DotNetNuke.HttpModules.Compression.CompressionModule, DotNetNuke.HttpModules" preCondition="managedHandler" />
<add name="RequestFilter" type="DotNetNuke.HttpModules.RequestFilter.RequestFilterModule, DotNetNuke.HttpModules" preCondition="managedHandler" />
<add name="Exception" type="DotNetNuke.HttpModules.Exceptions.ExceptionModule, DotNetNuke.HttpModules" preCondition="managedHandler" />
<add name="UsersOnline" type="DotNetNuke.HttpModules.UsersOnline.UsersOnlineModule, DotNetNuke.HttpModules" preCondition="managedHandler" />
<add name="DNNMembership" type="DotNetNuke.HttpModules.Membership.MembershipModule, DotNetNuke.HttpModules" preCondition="managedHandler" />
<add name="Personalization" type="DotNetNuke.HttpModules.Personalization.PersonalizationModule, DotNetNuke.HttpModules" preCondition="managedHandler" />
<add name="UrlRewrite" type="iFinity.DNN.Modules.UrlMaster.UrlRewriteModule, iFinity.UrlMaster.FriendlyUrlProvider" preCondition="managedHandler" />
</modules>