I am using out of the box items only!
I just updated to SharePoint 2010 SP1 Enterprise Edition June 2013 CU and I believe that BEFORE the update, I had this problem!
I go to my custom list, nothing major, no "custom" just local columns "items used" "important" "how many" ... basic stuff, text or choice fields.
I wanted to add some "flash" to it, so I edited the list, List TOols on the ribbon, List, Edit List, SharePoint Designer icon / button.
I wanted to add a conditional formatting item, say when AMount Feature used was say 3, but any changes causes error after I save the .aspx file in Designer and then go to the web browser.
In web browser, IE 9 on Windows 7 SP1 Enteprise Edition as a a farm administrator in browser, and sharepoint designer, I get this error:
open this Web page in a Microsoft SharePoint Foundation-compatible HTML editor
such as Microsoft SharePoint Designer. If the problem persists, contact your Web
server administrator.
ULS shows this:
Correlation
ID:aa8ce84d-aee0-4cd4-a197-145d4f465045
07/18/2013 14:28:26.84 w3wp.exe (0x15F8) 0x277C SharePoint Foundation Web Parts 89a1 High
Error while executing web part: System.NullReferenceException: Object reference not set to an instance of an object.
at System.Xml.Xsl.XslCompiledTransform.Load(MethodInfo executeMethod, Byte[] queryData, Type[] earlyBoundTypes)
at Microsoft.Xslt.STransform.GetCompiledTransform()
at Microsoft.SharePoint.WebPartPages.BaseXsltListWebPart.LoadXslCompiledTransform(WSSXmlUrlResolver someXmlResolver)
at Microsoft.SharePoint.WebPartPages.DataFormWebPart.GetXslCompiledTransform()
at Microsoft.SharePoint.WebPartPages.DataFormWebPart.PrepareAndPerformTransform(Boolean bDeferExecuteTransform) aa8ce84d-aee0-4cd4-a197-145d4f465045