If you receive the error of "Unable to open free/busy time" error when trying to access a shared calendar, try to refresh the user's free/busy information. This needs to be ran from the user that is sharing the calendar. You can refresh the free/busy information by running Outlook with the /CleanFreeBusy command-line switch on the computer that is having problems publishing free/busy information.
First, determine the path to Outlook by following these steps:
1. Click Start, point to Find and then click Files or Folders.
2. In the Named box, type Outlook.exe, and then click Find Now.
3. Note the path to the Outlook executable file for reference. For example, the default path is:
c:\Program Files\Microsoft Office\Office\Outlook.exe
4. On the File menu, click Close.
Next, run Outlook with the /CleanFreeBusy command-line switch, using the following steps:
1. Click Start, and click Run.
2. In the Open box, type the complete path noted earlier in step 3, including the file name. Press SPACEBAR and then type a forward slash (/) followed by the command-line switch, for example:
"c:\Program Files\Microsoft Office\Office\Outlook.exe." /CleanFreeBusy
NOTE: The full path needs to be in quotation marks to preserve long file names.