If you receive the error below, here is how to resolve it.
This means that Excel is set not to open a file extension it does not recognize. Since our templates, use a .XCT extension, this is a problem. This is not the default security setting in Excel, so someone has set it up this way. If you have a network administrator, you should let him or her know that to resolve the issue the following registry key needs to be changed to either 0 (=Disable check) or 1 (=Enable check and prompt). If you're having a problem, it is because it is currently set to 2 (=Enable check, no prompt deny open).
HKEY_CURRENT_USER\Software\Microsoft\Office\XX.0\Excel\Security\ExtensionHardening
where XX is your Office version number (15 for 2013, 14 for 2010 and 12 for 2007)
If you don't have a network administrator and don't want to play in the registry, here is a small program that we put together to change this setting:
You need to select either Disable check or Enable check and prompt (recommended) to resolve the issue.