Something that may solve this problem is to go through the following steps after this has failed for you (and your license details are empty):
1. Shut down Visual Studio without entering your license details (cancel out of the license pane, or choose the evaluation license)
2. Load up Visual Studio as an administrator (RunAs administrator)
3. Open up the license details, enter your license name and key
4. Click OK to save the license details
5. Shut down VS, then reload it as a non administrator
The forgetfulness of NCrunch is almost certainly caused by security constraints on your system or the activity of 3rd party software (i.e. virus scanners, registry cleaners, etc). Storing the details as an administrator reduces the risk of interference from the O/S security.