Patty,
XLB is a settings file format created by Microsoft Excel. XLB files contain:
* settings for the toolbars (or command bars). These settings can be edited or customized by selecting “toolbar” from the view options.
* information such as which toolbars are visible, their position, and their function.
* allow for the transfer of customization information between computers and users.
It sometimes gets corrupt and the only solution is to delete it.
By now we don't have a way to prevent it as it is a specific case.
Thanks
Diego