Thomson’s Answer to this question (which didn’t resolve my issue at all and they should have posted here, but apparently are too lazy to):
Thank you for contacting Thomson Reuters Technical Support.
This may happen when you try to save the compressed library within Program Files folder or even if the library files are placed inside the Program Files folder. Windows 7 will protect files in Program Files. Sometimes this issue may be related to permissions on your computer. Even though you have administrator rights Windows 7 applies stronger security to some locations.
When you create your .enlx file, where do you save it? Does it make a difference if you change your save location to the Desktop?
Please try to save the compressed library in the following location C:\Users[User Name]\Documents
If the library is inside the Program Files then I would also try to move the library to desktop and then make a compressed library. Let me know if you get the same error after moving the library to desktop or documents folder.
Each database consists of two files, *.enl and *.Data. Please make sure you both these files to same location.
If you are able to save the compressed library into the documents folder or desktop location then you may want to check the security setting for the location. Please see the following link for more information.
Note: You should contact Windows 7 technical support group before following instruction from the above link.
If the computer connected in a network then you should contact the network administrator.
If you cannot save the compress library on any location then sometimes the Administrator Account on Windows 7 may allow you to save the library. Please try to enable the Windows 7 administrator account and continue to make a compressed library.
Please see the following link to enable the administrator account.
In addition, Please note that EndNote libraries that exceed 4 GB in size and/or 65,535 files cannot be compressed using EndNote. Please refer the following Frequently Asked Questions page for more information on this:
If this is not the case, as a test, please open the sample library and try to backup it. You should be able to find the sample library in this location: C :/> Program Files>EndNote>Examples>Sample Library.
Please find the steps to backup the library in the link below,
If you are able to compress the sample library, then the issue might be with the specific library which you are trying to compress and having issue.
Please move a copy of your library to your desktop. Note that you should copy both the .enl and .data folder to the same location.
You might try to recover the library. Please find the instructions the link below,
Please let us know if you have any questions or if this does not resolve the issue and we will be happy to assist you.
Based on the information provided above, this case will be closed and no further action is required on your part. However, if this does not resolve your issue, please reply to this email and your case will be immediately reopened for additional support.