We have a bunch of network shares on which there are lots of Excel files, many of which contain macros necessary for functionality.  By default these locations are not trusted and the macros (and even editing a file) are blocked.  Fine.  Security reasons, I understand.  However, in previous versions of Office (2007 and back) I was able to add these locations as Trusted Locations.  In 2010, I cannot.  I have the "Allow Trusted Locations on my network" box checked, yet I am still unable to add them.  I continually get a message stating that "That path you have entered cannot be added as a Trusted Location for security reasons.  Choose another location or a specific folder."  I've tried selecting specific folders on the shares but that does not work either.  I've also tried adding the locations in the registry under HKCU\Software\Microsoft\Office\14.0\Excel\Security\Trusted Locations\ but that also does not work.

Any ideas?  I really need to be able to add these shares as Trusted Locations, because there are a lot of files that are used on a daily basis, and users are going to get irritated quickly if they have to click "Enable content" several times just to make a small change in a file...

There was a similar issue in Office 2007 when a root drive like X:\ was used as trusted location. (http://support.microsoft.com/kb/981041)

How do your trusted locations look like? How do you map network drives? Does it happen when you use \\server\share\path or \\ip_address\share\path or \\fqdn.domain.tld\share\path?

Some general hints: http://technet.microsoft.com/en-us/library/cc179039.aspx

Did you try to assign the locations with Group Policies?

On Windows XP the network drives are mapped using batch scripts at logon through Active Directory.  In Windows 7 the scripts do not consistently map drives.  I posted on the issue here, but it basically boils down to Windows 7 not recognizing cname aliases.  So, for Windows 7 I modified the script to use IP addresses (which do consistently work) and placed a copy in the Startup folder to map the drives.

Usually I just click the Browse button, find the drive (for example, M:\) and select it, and it adds the drive to my Trusted Locations.  When it shows up in the list of Trusted Locations it does not appear as M:\ but as \\server\share.

When I try the above technique in Office 2010, I get the error mentioned in my first post.  I tried adding the Trusted Locations through the registry as M:\ and as \\server_IP\share and neither one worked.  When I looked at the list of Trusted Locations, the one I added was grayed out and I could not even select it.  Opening spreadsheets from the location still blocked macros.  I did not try adding the location as \\server\share since the drive mapping script does not work using that format.

Anybody ever find a solution?

Really?  Nobody has any other advice to offer?

Bumping won't solve it ;) Maybe you should insert a coin somewhere ...

One possible cause could be that your M: is identified as "Internet Zone". Try adding your server in different ways as Trusted Sites (in Internet Explorer):

file://server
http://server

with server = netbios name, ip address and fqdn

No luck.  Adding the server to the Trusted Sites didn't allow me to add them to the Trusted Locations in Office.  Great work, MS, on f-ing up yet more things that used to work perfectly fine...

I had the same problem and considering all my work is in Excel files stored in our network shared drive it was getting pretty frustrating. This is how I solved it for Excel 2010.

1. Go to Excel Options > Trust Center > Trust Center Settings
2. Go to 'Protected View' on the left hand side tab.
3. Uncheck the box which says 'Enable Protected View for files originating from the Internet'

 Please note that the above method has an obvious security risk but if you are wise enough you should be fine.

Did you try adding server as \\servername.domain.com?  Using the IP address did not work, but using the entire name such as "\\server01.bacon.com" worked for me.