When you've just got the game for the first time, Windows Defender or your Antivirus can prevent it from starting. Just tell Windows Defender or your Antivirus that the Promotion Wars - 21st Anniversary Edition.exe file can be trusted, and re-open the game.
Changing the language in Windows to English tends to avoid getting error messages in the game / editor.
Also check the Windows setting:
Administrative Language Settings > Formats
Make sure the Format is set to English.
This can happen when your Windows language isn't set to English - see the question regarding that, for how you can fix it easily.
This can happen when a recent Data Pack is played on a version of the game from before October 2022. On that date, big changes were made to the file structures, so to avoid this error, simply make sure you're always using the latest version of the game (here).
If this shows the first time you try to play, make sure that you downloaded the Full Install, not the Basic Download. The installation program puts this file on your system and registers it. If your anti-virus flagged up an error during the install, the required system files may have been blocked from installing. If that happens, you should tell your anti-virus that the installer file can be trusted, then run the installer again.
If the error shows after you've been playing the game okay, it may be that your Antivirus or Windows Defender has quarantined the file. If so, tell your Antivirus or Windows Defender to trust the file. You may then need to re-install the game, to make sure the file is where it needs to be.
This can happen if you've installed the game in the Program Files folder and are not running the program as an administrator.
When you play the game from the Program Files folder, right click on 'Promotion Wars - 21st Anniversary Edition.exe' and choose run as administrator.
Alternatively, install the game to a different folder of your laptop or PC and this shouldn't happen anymore.
Promotion Wars: 21st Anniversary Edition supports images in the formats .jpg, .gif and .bmp. If any other type of image - such as .png, .jpeg - is renamed to one of those three types, it will cause this error message. Use an image editor (or Paint) to properly save the image as a .jpg, .gif or .bmp file.
This can happen if you've got the game in the Program Files folder, due to it only allowing the Administrator to create new files in that location. Simply move your game folder to somewhere else, such as the C Drive, and this problem won't occur.
Post any other errors in the relevant section of the PW Arena and I will resolve the issue as quickly as possible.