A number of reasons can cause this problem. From a newsgroup post:
Reason 1: Large .pst or .ost file.
Are you using a large .pst or .ost file? If your .pst or .ost file is larger than 2GB, you may experience a performance issue in Outlook 2007. In order to accommodate new features Outlook 2007 introduced a new data structure for .pst and .ost files. In this new data structure the frequency of writing data to the hard disk increases as the number of items in the .pst or .ost files increases.
To resolve this problem use one of the following methods:
- Reduce the size of the Exchange mailbox.
- Use an online mode profile instead of a cached mode profile.
- Split your large .pst file into several smaller .pst files.
- Use a filter to restrict the items that you synchronized from Exchange into your .ost file.
For more information, please refer to ME932086
Reason 2: Windows Desktop Search 3.0.
Have you installed any desktop search engine such as Windows Desktop Search 3.0? If this is the case, please temporarily uninstall it and then test the issue.
If this does not match your situation then please also try some suggestions below to narrow it down:
- Temporarily turn off/remove antivirus program. Many times such issue can be caused by the antivirus program currently running on the machine. Please temporarily turn off or remove antivirus application and see if this scenario is gone.
- Temporarily remove Adobe Reader. Sometimes Adobe Reader can also cause this issue. If you have this program installed on your computer please temporarily remove it and see if this issue can be resolved.
- Test in Outlook Safe Mode. Outlook Safe Mode can narrow down issues which are caused by any extensions corrupted resources files registries or templates. Click Start -> Run. In the Open box type: "Outlook /safe" (without the quotation marks).