Error when converting Lead to Opportunity in CRM 3.0

We just did several custom attributes and fields in the Lead and Opportunity forms.

Now, when we try to convert the lead to opportunity, we get the following error:

Server Error in '/' Application.
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The string was not recognized as a valid DateTime. There is a unknown word starting at index 3.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.FormatException: The string was not recognized as a valid DateTime. There is a unknown word starting at index 3.

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.  

Stack Trace:


[FormatException: The string was not recognized as a valid DateTime.  There is a unknown word starting at index 3.]
   System.DateTimeParse.Lex(Int32 dps, __DTString str, DateTimeToken dtok, DateTimeRawInfo raw, DateTimeResult result, DateTimeFormatInfo& dtfi) +1658
   System.DateTimeParse.Parse(String s, DateTimeFormatInfo dtfi, DateTimeStyles styles) +334
   System.DateTime.Parse(String s, IFormatProvider provider, DateTimeStyles styles) +30
   Microsoft.Crm.BusinessEntities.CrmDateTime.Deserialize(String serializedForm, String formattedDate, String formattedTime) +106
   Microsoft.Crm.BusinessEntities.EntityDeserializationStrategyBase.GetAttributeValue(EntityDeserializationContext context, AttributeMetadata attributeMetadata, String attributeValueText, IDictionary subAttributes) +179
   Microsoft.Crm.BusinessEntities.AttributeInfo.Deserialize(EntityDeserializationContext context, IEntityDeserializationStrategy deserializationStrategy) +541
   Microsoft.Crm.BusinessEntities.BusinessEntity.ReadAttribute(EntityDeserializationContext context, IEntityDeserializationStrategy deserializationStrategy, String attributeName) +46
   Microsoft.Crm.BusinessEntities.BusinessEntity.DeserializeAttributes(EntityDeserializationContext context, IEntityDeserializationStrategy deserializationStrategy) +41
   Microsoft.Crm.BusinessEntities.BusinessEntity.Deserialize(XmlReader reader, IEntityDeserializationStrategy deserializationStrategy) +146
   Microsoft.Crm.BusinessEntities.BusinessEntity.Deserialize(String entityXml, IEntityDeserializationStrategy deserializationStrategy) +86
   Microsoft.Crm.BusinessEntities.BusinessEntity.Deserialize(String entityXml) +26
   Microsoft.Crm.Application.Platform.Entity.CreateFrom(Int32 sourceEntityType, String sourceEntityId, TransformType transformType) +497
   Microsoft.Crm.Web.SFA.LeadDetailPage.Qualify(Object sender, DataEventArgs e) +430
   Microsoft.Crm.Application.Forms.DataEventProcessor.Raise(FormEventId eventId, FormState state, User user, String objectId, Entity entity) +176
   Microsoft.Crm.Application.Forms.AppForm.RaiseDataEvent(FormEventId eventId) +89
   Microsoft.Crm.Application.Forms.EndUserForm.Initialize(Entity entity) +56
   Microsoft.Crm.Application.Forms.CustomizableForm.Execute(Entity entity, String formId, String formType) +83
   Microsoft.Crm.Application.Forms.CustomizableForm.Execute(Entity entity) +13
   Microsoft.Crm.Web.SFA.LeadDetailPage.ConfigureForm() +346
   Microsoft.Crm.Application.Controls.AppPage.OnPreRender(EventArgs e) +29
   System.Web.UI.Control.PreRenderRecursiveInternal() +62
   System.Web.UI.Page.ProcessRequestMain() +1499

 
Looks like there's a problem with one of the dates, but  can't find the source.

The lead also goes to 'Closed Leads' but does not move to opportunities....

Any ideas?
Convert-Error.pdf