Matt,

Just upgraded to 4.5.2.  Then added a new property to my home page doctype did a save and got

Input string was not in a correct format.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: Input string was not in a correct format.

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: Input string was not in a correct format.]
   System.Number.StringToNumber(String str, NumberStyles options, NumberBuffer& number, NumberFormatInfo info, Boolean parseDecimal) +9594283
   System.Number.ParseInt32(String s, NumberStyles style, NumberFormatInfo info) +119
   System.Convert.ToInt32(String value) +48
   TheOutfield.UmbExt.AutoExport2DotNet.AppBase.DocumentType_ExportCode(DocumentType sender, EventArgs e) +378
   umbraco.cms.businesslogic.web.DocumentType.FireAfterSave(SaveEventArgs e) +75
   umbraco.cms.businesslogic.web.DocumentType.Save() +129
   umbraco.settings.EditContentTypeNew.OnBubbleEvent(Object source, EventArgs args) +402
   System.Web.UI.Control.RaiseBubbleEvent(Object source, EventArgs args) +37
   umbraco.controls.ContentTypeControlNew.save_click(Object sender, ImageClickEventArgs e) +427
   System.Web.UI.WebControls.ImageButton.OnClick(ImageClickEventArgs e) +115
   System.Web.UI.WebControls.ImageButton.RaisePostBackEvent(String eventArgument) +120
   System.Web.UI.WebControls.ImageButton.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) +5563

Regards

Ismail