Invalid character

Invalid character is a term that covers a few possibilities.

Neverwinter Nights
For NWN in general, it usually indicates a corrupt character or one that violates ELC. You cannot log into BoW with such character and need to report them in order to have them removed from your server vault.

Bastions of War
In BoW, invalid characters are ones that violate character creation or other rules. Characters can be invalidated on BoW by:
 * Taking the Pick Pocket skill during character creation
 * Twinking
 * Creating a character with an invalid name
 * Player or DM requested deletion

Invalid characters are removed from the server vault within 24 hours.

Test characters are also technically considered invalid, but they're treated differently, i.e., not deleted and allowed in the Test Tent.