Error: Guid should contain 32 digits with 4 dashes (xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx)

The Content Editor Web Part occasionally gives me this error when it contains HTML source and it doesn't like something in the HTML source after it has parsed (changed) the HTML source. Once this happens, the page is uneditable and the problem is not able to be easily rectified.

Exact steps to reproduce would be:

1. Add a Content Editor Web Part.
2. Insert some simple HTML source with an embedded <span style="color:blue">TEST</span> in there.
3. Save and approve the page.
4. Edit the page.
5. Attempt to edit the web part. You will receive a JavaScript error stating that "style.display is null or not an object".
6. Attempt to delete the web part. You will receive the following error below.

Server Error in '/' Application.
--

Guid should contain 32 digits with 4 dashes (xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx).

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: Guid should contain 32 digits with 4 dashes (xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx).

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: Guid should contain 32 digits with 4 dashes (xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx).]
System.Guid..ctor(String g) +2957
Microsoft.SharePoint.WebPartPages.SPWebPartManager.ApplyChangeList(String changeString) +1237
Microsoft.SharePoint.WebPartPages.SPWebPartManager.OnLoad(EventArgs e) +712
System.Web.UI.Control.LoadRecursive() +101
System.Web.UI.Control.LoadRecursive() +211
System.Web.UI.Control.LoadRecursive() +211
System.Web.UI.Control.LoadRecursive() +211
System.Web.UI.Control.LoadRecursive() +211
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +2588

--
Version Information: Microsoft .NET Framework Version:2.0.50727.42; ASP.NET Version:2.0.50727.210

[2573 byte] By [HectorMike] at [2008-1-10]