According to a couple of threads here it seems that there may be some type of conflict or corruption that causes this problem. The first thing to try would be to un-install the extension then install it again. If you are prompted to overwrite any existing files select 'yes to all'.
If this does not work for you there may be an issue with the configuration and it would need to be deleted, then re-install DataAssist selecting 'yes to all' again if prompted. Here is a link to a thread that discuses the process for removing the config:
Please let us know if the issue persists.