That is not much information for being able to help you.

1. What version of UltraCompare is used by you?
2. Which user interface mode is used by you – the ribbon mode or the toolbar/menu mode?
3. What type of comparison do you run – a text file comparison, a binary file comparison, a folder comparison, or a table comparison, a PDF file comparison?
4. Is a file or folder opened at all in both panes?
5. Is All selected in menu View on using toolbar/menu mode respectively in first group Show on ribbon tab Edit on using ribbon mode?
6. Are Ignore options enabled on ribbon tab View or in the menu Options in submenu File Ignore Options?

It would be best making a screenshot of the entire UltraCompare application window with Alt+Break which is saved as PNG image file. The PNG image file should be uploaded as attachment to your next post after clicking on button Full Editor & Preview in web browser for being able to attach a PNG file with the drag and drop area at the bottom of the displayed page or using the button Add files.

It looks like the two compared files C:\temp\RefreshSaves\XP_QWICKLY.sql and C:\temp\RefreshSaves\XP_QWICKLY_TEST.sql are two empty files with file size 0 for both files.

1. Are these two files also opened in UltraEdit or are two files with different file names opened in UltraEdit and UltraEdit created temporary files for comparing them with UltraCompare?
2. Is the option Compare selected text checked in the Compare Files/Folders dialog window of UltraEdit although no text is selected in both opened files?
3. What is selected for configuration setting Use temporary file for editing (provided for very large file handling) in UltraEdit at Advanced - Settings or Configuration - File handling - Large files (UE ≥ 2023.1) or Advanced - Settings or Configuration - File handling - Temporary files (UE < 2023.1)?
4. What are the file sizes of the two files opened in UltraEdit shown at the bottom on the status bar?
   Multi-gigabyte files can be compared with UltraCompare Professional. UltraCompare Lite does not have a hard-coded limit on file size, but several items factor into whether or not the compare can be executed in UC Lite, including file size, amount of difference blocks, memory required to map them, etc.
5. Which version of UltraEdit is used by you?
6. Is UltraCompare Professional installed and started by UltraEdit or is UltraCompare Lite started by UltraEdit as installed together with UltraEdit?
   There is displayed at bottom of the Compare Files/Folders dialog window of UltraEdit the note "You are using UltraCompare Lite." on using UltraCompare Lite installed with UltraEdit.

That's fine.

It looks like that happened also other users of UltraEdit. There is shown by UltraEdit for Windows v2024.0.0.35 a message box with the following text on checking Compare selected text in the Compare Files/Folders dialog window and clicking next on button Compare and nothing is selected in the last used files:

In order to use the feature 'Compare highlighted text,' text must be highlighted in each file to be compared.

The text comparison is not started in this case by UltraEdit.

Well, the information is not 100% correct as highlighted and selected are two different things in UltraEdit/UEStudio. I will send an email to UltraEdit support with a suggestion for a better information like:

In order to use the feature 'Compare selected text', text must be selected in each file to be compared.