This issue may be caused by corrupted user configuration, to fix it the user config file should be deleted.

Close FIXEye
Remove user config file
C:\Users\<user>\AppData\Local\B2BITS\FIXEye\FIXEye.user.config
Restart the application.

Verify that the message contains the valid FIX messages with the "␁" as a delimiter.

FIXEye 4.2 supports only "␁" as a delimiter.

Verify that the FIX messages are not split across multiple lines inside the files to compare.

Browser not supported