I am running DNN 7.3.4. I have a required user profile property. Everything works fine if the user registers themselves, but if I create the user as the admin and they try to login they get an error. Here is the text from the error log:

System.FormatException occurred
HResult=-2146233033
Message=Input string was not in a correct format.
Source=mscorlib
StackTrace:
at System.Number.StringToNumber(String str, NumberStyles options, NumberBuffer& number, NumberFormatInfo info, Boolean parseDecimal)
at System.Number.ParseInt32(String s, NumberStyles style, NumberFormatInfo info)
at System.String.System.IConvertible.ToInt32(IFormatProvider provider)
at System.Convert.ToInt32(Object value)
at DotNetNuke.UI.WebControls.DNNListEditControl.RenderViewMode(HtmlTextWriter writer)
at DotNetNuke.UI.WebControls.EditControl.Render(HtmlTextWriter writer)
at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter)
at System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter)
at System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
at System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children)
at System.Web.UI.Control.RenderChildren(HtmlTextWriter writer)
at System.Web.UI.WebControls.WebControl.RenderContents(HtmlTextWriter writer)
at System.Web.UI.WebControls.WebControl.Render(HtmlTextWriter writer)
at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter)
at System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter)
at System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
at System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children)
at System.Web.UI.Control.RenderChildren(HtmlTextWriter writer)
at System.Web.UI.WebControls.WebControl.RenderContents(HtmlTextWriter writer)
at System.Web.UI.WebControls.WebControl.Render(HtmlTextWriter writer)
at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter)
at System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter)
at System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
at System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children)
at System.Web.UI.Control.RenderChildren(HtmlTextWriter writer)
at System.Web.UI.HtmlControls.HtmlContainerControl.Render(HtmlTextWriter writer)
at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter)
at System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter)
at System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
at System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children)
at System.Web.UI.Control.RenderChildren(HtmlTextWriter writer)
at System.Web.UI.WebControls.WebControl.RenderContents(HtmlTextWriter writer)
at System.Web.UI.WebControls.WebControl.Render(HtmlTextWriter writer)
at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter)
at System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter)
at System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
at ASP.desktopmodules_admin_security_profile_ascx.__Render__control1(HtmlTextWriter __w, Control parameterContainer) in c:\inetpub\wwwroot\uujec\DesktopModules\Admin\Security\Profile.ascx:line 8
InnerException:

Further testing shows that adding the required flag on a profile property does not break logins for users who have logged in previously. In that situation it will stop and ask the user to fill in the missing properties. But if the user was created by an admin account and they have never logged in, then when they try to log in it doesn't ask them to fill in the profile properties. It just throws the error above.

This is the code where the error is occurring in Profile.ascx:
function setUpProfile() {
$('.dnnButtonDropdown').dnnSettingDropdown();
$('#<%=ProfileProperties.ClientID%>').dnnPanels(); // This is where it breaks.
}

The profile property is just a text field, not a date or int, so I don't understand why it would say "Input string was not in a correct format". This only happens to users created by an Admin account, not users who registered themselves.

You can report this as a bug at support.dotnetnuke.com.