I suggest you to use some methods to fix .dbx files...
1. Using the Compacting method.
To start, follow these steps:
-In Outlook Express, click Work Offline on the File menu to terminate any transmission.
-In the Folder list, click on Outlook Express to ensure that no email or news folder is opened.
-Close the Folder list by click the X in the upper right-hand corner of the list panel.
-On the File menu, select Folder, and then select Compact All Folders.
This might take several minutes.
-If an error occurs, close Outlook Express, re-open it, and begin the process again from the top.