If you receive an "unable to open document" error when attempting to open a .TIF file in Microsoft Outlook 2007 or 2010, it may be due to a limitation on the number of documents Windows can save in the "Temporary Internet Files/OLKE" folder.
The limit for this folder seems to be 100 files, so after downloading your 100th attachment, you will be presented with this error message until you purge the contents of the folder.
In our case, the contents of the folder looked like this (as it was a fax mailbox):
fax.tif(97), fax.tif(98) and fax.tif(99)
In order to resolve this issue, you need to go and delete some of these files using the following steps:
- Find the location of the folder in which these files are stored by navigating to the registry (Start, Run, RegEdit) and finding the following key: HKEY_CURRENT_USER > Software > Microsoft > Office > 14.0 > Outlook > Security > Value Name: OutlookSecureTempFolder > Value Type: REG_SZ > Value Data: Temporary Internet Files
- Copy the value to an explorer window, delete all files in the folder.
For Example: 'C:\Documents and Settings\user name\LOCAL Settings\Temporary Internet Files\OLK18F'
N.B: The exact registry location will vary depending on your version of Windows. See below for an example on Windows 7.
Once you've deleted these files, restart Outlook and the problem should be resolved.
If you need more help, the official Microsoft knowledgebase article covering this issue can be found here.