The 7500E calculates worked time between punches and accumulated totals on the card for a pay period using E-7 Cards. If the display shows E-05 when inserting a card this is due to improper feeding of the time card. There is either a jam or more likely using a time card that is out of specification(too thin, too thick, gloss stock, etc.).
The resolution would be to ensure that Lathem branded E-7 cards are used as they are designed specifically as part of the system to ensure proper operation. Counterfeit cards are likely to cause problems with the device and will void the original warranty.
If you are using Lathem branded E-7 cards and are still having issues please contact support at 404-691-1064.