Yep, and tried that, same error:

Exception occurred creating type 'MindFusion.Scheduling.WinForms.Calendar, Calendar, Version=4.0.2357.25124, Culture=neutral, PublicKeyToken=123456789abcdef' System.ComponentModel.LicenseException: Couldn't get design-time license for 'MindFusion.Scheduling.WinForms.Calendar'
licenses.licx Line 1

Staying with the current Planner.NET 4, I have downloaded a great tool from Microsoft called "Process Monitor" (http://technet.microsoft.com/en-us/sysinternals/bb896645) and used it to monitor registry reads when Visual Studio was doing the build. After filtering the log file, I found the following:

16:36:13.5196366
LC.exe
1048
RegOpenKey
HKLM\Software\Wow6432Node\MindFusion Limited\ComponentLicenses
SUCCESS
Desired Access: Read

16:36:13.5196832
LC.exe
1048
RegSetInfoKey
HKLM\SOFTWARE\Wow6432Node\MindFusion Limited\ComponentLicenses
SUCCESS
KeySetInformationClass: KeySetHandleTagsInformation, Length: 0

16:36:13.5197025
LC.exe
1048
RegQueryValue
HKLM\SOFTWARE\Wow6432Node\MindFusion Limited\ComponentLicenses\MindFusion.Scheduling.WinForms.Calendar
NAME NOT FOUND
Length: 144

Then I noticed that LC.exe is looking for "MindFusion.Scheduling.WinForms.Calendar" and not "Planner.NET" as I expected.

I then ran Process Monitor on the old build machine and compared the log files. This confirmed that "MindFusion.Scheduling.WinForms.Calendar" is the correct registry string that I should have.

A quick check in the old machine's registry for the value, and hey presto! My build now works.

Many thanks for your help . I can go home happy now