An error occurred while communicating with the server. Please try again
An error stating An error occurred while communicating with the server. Please try again may occur in a modal window inside WHMCS and look like this:

This guide provides troubleshooting steps to identify and resolve the underlying causes of this message.
System URL Mismatch
1. Make a note of the URL displayed in your browser on the page experiencing the error

2. Navigate to Configuration > System Setup > General Settings > General tab
3. Ensure the WHMCS System URL value is the same as the URL observed in step 1:

If they do not match:
Ensure you access the Admin Area using the URL specified in the WHMCS System URL Setting,
or
Update the WHMCS System URL Setting to match the URL you are using to access the Admin Area
PHP Fatal Error
A PHP error could be occurring. To capture the error details:
1. Navigate to Configuration > System Setup > General Settings > Other tab
2. Enable the Log Errors option
3. Click Save Changes
4. Reproduce the problem
5. Navigate to Configuration > System Logs and look for the error details.
Another Error Type
If no error is logged, then your browser's network analyser tool can be used to identify the underlying error in the modal popup:
1. Navigate to the page experiencing the error
2. Right click on a blank space on the page and select Inspect (the exact label may vary depending upon your browser)

3. Click on the Network tab:

4. Now reproduce the error
5. A number of entries will appear in the Name column. Click on the entry which appears at the same time
6. Click on the Response sub-tab:

7. Observe the code which is displayed in the Response sub-tab.
This will contain details of the error that is occurring.