I downloaded the latest version of the Data Zoom installer and followed the directions to install he .wsp. Everything went find and it installed properly. However I am getting a references error when I go to add the web part to a page.
After some digging and comparing it to another install that I had done, I noticed the .resx files were missing from the \App_GlobalResources directory. I copied the files from a previous install and it works fine now.
Why were these files not installed in the first place??
Unfortunately SharePoint doesn't provide a way to install .resx files to the App_GlobalResources directory using a SharePoint Solution package. As a result the files are copied to the App_GlobalResources directory by a feature receiver. The feature receiver tries to copy the files to the appropriate location as the application pool identity. Some shops have tightened the security granted by the application pool identity which requires write access to the App_GlobalResources directory. You can also correct this issue by granting write access to the WSS_WPG group and re-activating the feature.