eAuthorize 3.5 connection problems

Begin by making sure the plugin is installed correctly. You can verify this by opening the FileMaker application preferences and going to the plugins tab. Make sure eAuthorize is showing up on the list of available plugins. From there, you should also be able to select the plugin, click configure, and enter the registration code (until then the plugin will remain in demo mode).
If the plugin appears correctly on the list, the next step would be to try using some of our example files that come with our download to test the plugin. In our eAuthorize download folder, open the Authorize.net or Verisign folder (depending on which you are trying to connect to). Inside that folder you will find a folder named Integration Files. Open it and and you will find two filemaker databases named eAuthorize_BlackBox.fp5 and Sales-BlackBox.fp5. Open both of these in FileMaker.
On the eAuthorize_BlackBox.fp5 file, you will find the login and password fields. It would be best to begin by trying transactions with the test login we provided. The Sales-BlackBox.fp5 file is where you can enter a card number, amount, and expiration and run the transaction. If the transactions with the test account are successful, then the connectivity between the plugin and the gateway is good. Once the connectivity has been verified, you switch to an account of your own (if you have one set up).
The benefit of doing this troubleshooting is that the bottom of the Sales-BlackBox.fp5 file has a detailed listing of the transaction that ran. If there was an error it will give you the response text in one of the fields so you can tell exactly why it failed and act accordingly.