TestComplete displays this message when you open a project or project suite that was created in an earlier version of TestComplete and contains logs. The log files format in TestComplete 15 has been changed slightly, so TestComplete needs to convert the log files to the new format in order for you to be able to use these logs. Note that after converting the log files, they become incompatible with earlier versions of TestComplete, so you will be unable to open them in earlier versions of TestComplete.
To convert the project (project suite) logs to the new format, click Yes. To convert the old-format log files in all projects of the current project suite, click Yes to All. If you press No, TestComplete will leave the old-format logs unchanged and remove links to these logs from the project. To remove links to logs with the old format from all projects of the current project suite, press No to All.