1. Created a multi-step contour form in one pass and applied it to a page using richtext editor and published the page (http://www.logotukku.fi/tilaa.aspx)

2. When testing the form, filled the first step fields and clicked "next". Filled the second step fields and clicked 'previous'.

The page fails with following error message: 'Input string was not in a correct format.'

[FormatException: Input string was not in a correct format.]
System.Number.StringToNumber(String str, NumberStyles options, NumberBuffer& number, NumberFormatInfo info, Boolean parseDecimal) +7469351
System.Number.ParseInt32(String s, NumberStyles style, NumberFormatInfo info) +119
System.String.System.IConvertible.ToInt32(IFormatProvider provider) +46
System.Convert.ToInt32(Object value) +28
umbraco.providers.members.UmbracoMembershipProvider.GetUser(Object providerUserKey, Boolean userIsOnline) in d:\TeamCity\buildAgent\work\7380c184e9fcd3ea\umbraco\providers\members\MembersMembershipProvider.cs:605
System.Web.Security.Membership.GetUser(Object providerUserKey, Boolean userIsOnline) +61
System.Web.Security.Membership.GetUser(Object providerUserKey) +6
Umbraco.Forms.Core.Record.ToXml(XmlDocument xd) in d:\TeamCity\buildAgent\work\39da791f9304089a\Umbraco.Forms.Core\Record.cs:51
Umbraco.Forms.Data.Storage.RecordStorage.UpdateRecordXml(Record record, Form form) in d:\TeamCity\buildAgent\work\39da791f9304089a\Umbraco.Forms.Core\Data\RecordStorage\RecordStorage.cs:208
Umbraco.Forms.Data.Storage.RecordStorage.UpdateRecord(Record record, Form form) in d:\TeamCity\buildAgent\work\39da791f9304089a\Umbraco.Forms.Core\Data\RecordStorage\RecordStorage.cs:185
Umbraco.Forms.Core.Services.RecordService.SaveRecord() in d:\TeamCity\buildAgent\work\39da791f9304089a\Umbraco.Forms.Core\Services\RecordService\RecordService.cs:328
Umbraco.Forms.UI.Usercontrols.RenderForm.prevPage(Object sender, EventArgs e) in d:\TeamCity\buildAgent\work\39da791f9304089a\Umbraco.Forms.UI\Usercontrols\RenderForm.ascx.cs:193
System.Web.UI.WebControls.Button.OnClick(EventArgs e) +111
System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) +110
System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +10
System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +13
System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +36
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1565

4. Deleted and rebuild the form and the page, with same results.

Background information: Windows 2003 Server with SQL Server 2005. Umbraco 4.0.3 with Contour license.