When you use Microsoft Outlook, you may experience either of the following symptoms:

•	When you try to create a new task or a new appointment, you receive an error message that is similar to the following error message: Could not complete the operation. One or more parameter values are not valid.
•	When you try to quit Outlook, you receive the following error message: An extension failed to initialize. Can't open file: extend.dat. The file may not exist, you may not have permission to open it, or it may be open in another program.

Back to the top

This problem may occur if the profile or the data files that Outlook uses are corrupted.

If you received the "An extension failed to initialize" error message that is mentioned in the "Symptoms" section, the file attribute is set to hidden for the Extend.dat and Outcmd.dat files.

Back to the top

To resolve this problem, follow these steps in the order that they are presented.

Back to the top

Part 1: Create a New Profile

Note Because there are several versions of Microsoft Windows, the following steps may be different on your computer. If they are, see your product documentation to complete these steps.

1.	Click Start, and then click Control Panel.
2.	If you are not in Classic view, click Switch to Classic View, and then double-click Mail.
3.	Click Show Profiles.
4.	Click Prompt for a profile to be used, and then click Add.
5.	In the Profile Name box, type a descriptive name for the new profile, and then click OK.
6.	Click Add a new e-mail account, and then click Next.
7.	Click the appropriate server type for your new e-mail account, and then click Next.
8.	Follow the instructions that appear on the screen, and then click Finish. Note Make sure that you specify a new personal folder file (.pst file). Do not use the existing file.
9.	Click OK.

Note Because you do not use the old .pst file while you are troubleshooting, you will not see any of your old .pst folders or files.

Back to the top

Part 2: Rename the Outlook Data Files

Outlook automatically replaces the Extend.dat data file, the Outcmd.dat data file, and the Frmcache.dat data file if these files are missing. To rename the data files and then test to see whether the problem is resolved, follow these steps:

Note Because there are several versions of Microsoft Windows, the following steps may be different on your computer. If they are, see your product documentation to complete these steps.

1.	Quit all programs.
2.	Click Start, and then click Search.
3.	Click All files and folders.
4.	In the All or part of the file name box, type extend.dat, outcmd.dat, frmcache.dat.
5.	In the Look in box, click Local Hard Drives.
6.	Click More advanced options.
7.	Click to select the Search hidden files and folders check box.
8.	Click Search to search for the files. By default, these files are located in the following folders, where drive is the drive where Windows is installed. File Name Default Location Outcmd.dat drive:\Documents and Settings\user\Application Data\Microsoft\Outlook Extend.dat drive:\Documents and Settings\user\Local Settings\Application Data\Microsoft\Outlook Frmcache.dat drive:\Documents and Settings\user\Local Settings\Application Data\Microsoft\FORMS
9.	For each file that appears in the Search Results dialog box, right-click the file, click Rename, type a new name for the file (for example, type extend.old), and then press ENTER.
10.	Close the Search Results dialog box.
11.	Start Outlook.
12.	When you are prompted, click the new profile.
13.	Create a new task or a new appointment to see whether the problem is resolved.

Note Outcmd.dat stores any custom changes that you make to your toolbar buttons. If the problem is resolved after you rename this file, you must make the custom toolbar button changes again.

Back to the top

If you received the "An extension failed to initialize" error message that is mentioned in the "Symptoms" section, remove the hidden attribute on the Extend.dat and Outcmd.dat files.

Back to the top

If the problem is resolved and you use a .pst file in the new profile and the old profile, change the new profile to use the old .pst file, or import the contents of the old .pst file to the new .pst file.

For more information about how to create a new set of .pst files, click the following article number to view the article in the Microsoft Knowledge Base: For more information about other causes for this error, click the following article number to view the article in the Microsoft Knowledge Base: For more information about how to create profiles in Outlook 2002, click the following article number to view the article in the Microsoft Knowledge Base:

Back to the top