|2756 - The property '' was used as a directory property in one or more tables, but no value was ever assigned|
You have used a directory key which doesn't exist (in the "Directory" table). One common reason for this is that you got the case wrong, for example if you used "Windowsfolder" instead of "WindowsFolder".
If this is an msi you built then the fact that you are getting this error while installing the msi implies that you may not have performed MSI validation or that you ignored the generated message (review your procedures!).