I am receiving the error below when I attempt to associate any
workflow to any list.

Unable to validate data. at
System.Web.Configuration.MachineKeySection.GetDecodedData(Byte[] buf,
Byte[] modifier, Int32 start, Int32 length, Int32& dataLength)
at System.Web.UI.ObjectStateFormatter.Deserialize(String
inputString)

I have done several changes to the environment since the last known
good state. Started showing up on two development servers. Any
suggestions?

Except from the log below.

12/02/2008 15:51:45.54 w3wp.exe (0x0CF0)
0x1628 Windows SharePoint Services
General 6t8b Verbose
Looking up context site
http://itsslabvm25:80/_layouts/ItemRWfAssoc.aspx?List=%7B9F0F20E0-
BE1C-4C05-9219-9D5F83418132%7D in the farm SharePoint_Config_1b1a02eb-
f30f-4d64-962f-0e0f6909d0f8
12/02/2008 15:51:45.54 w3wp.exe (0x0CF0)
0x1628 Windows SharePoint Services
General 6t8d Verbose
Looking up the additional information about the typical site
http://itsslabvm25:80/_layouts/ItemRWfAssoc.aspx?List=%7B9F0F20E0-
BE1C-4C05-9219-9D5F83418132%7D.
12/02/2008 15:51:45.54 w3wp.exe (0x0CF0)
0x1628 Windows SharePoint Services
General 6t8f Verbose Site
lookup is replacing http://itsslabvm25:80/_layouts/ItemRWfAssoc.aspx?
List=%7B9F0F20E0-BE1C-4C05-9219-9D5F83418132%7D with the alternate
access url http://itsslabvm25.
12/02/2008 15:51:45.54 w3wp.exe (0x0CF0)
0x1628 Windows SharePoint Services
General 6t8g Verbose
Looking up typical site
http://itsslabvm25:80/_layouts/ItemRWfAssoc.aspx?List=%7B9F0F20E0-
BE1C-4C05-9219-9D5F83418132%7D in web application SPWebApplication
Name=SharePoint - 80 Parent=SPWebService.
12/02/2008 15:51:45.54 w3wp.exe (0x0CF0)
0x1628 Windows SharePoint Services
General 6t8h Verbose Found
typical site / (4082045a-2091-448c-88c1-564288879b18) in web
application SPWebApplication Name=SharePoint - 80 Parent=SPWebService.

12/02/2008 15:51:47.76 w3wp.exe (0x0CF0)
0x1628 Windows SharePoint Services
General 8nca Verbose
Application error when access /_layouts/ItemRWfAssoc.aspx,
Error=Unable to validate data. at
System.Web.Configuration.MachineKeySection.GetDecodedData(Byte[] buf,
Byte[] modifier, Int32 start, Int32 length, Int32& dataLength) at
System.Web.UI.ObjectStateFormatter.Deserialize(String inputString)

12/02/2008 15:51:47.82 w3wp.exe (0x0CF0)
0x1628 Windows SharePoint Services
General 0 Verbose
Releasing SPRequest with allocation Id {8020598D-6D93-4A78-
9D06-2976CA39757F}
12/02/2008 15:51:47.82 w3wp.exe (0x0CF0)
0x1628 Windows SharePoint Services
General 0 Verbose
Releasing SPRequest with allocation Id {DCE334EA-82B2-441B-
9BEC-C800E362C4F5}