Reorganized debtor objected to an application for payment of administrative claims that was filed by debtor's former in-house counsel ("Counsel"), purportedly on his own behalf and on behalf of more than 200 former employees of debtor. The application was filed on the last possible day to file administrative claims, and sought allowance of severance and layoff benefit claims as administrative expenses pursuant to 11 U.S.C. § 503(a) and (b). Counsel had no attorney-client relationship with the employees, did not obtain express authorizations to file claims on the employees' behalf, did not send the listed employees copies of the application that was filed, and subsequently withdrew his personal claim and his "representation" of the employees. The court determined that the application was not a class certification but, rather, a "class claim," which is not permitted in the Tenth Circuit pursuant to Sheftelman v. Standard Metals Corp. (In re Standard Metals Corp.), 817 F.2d 625, 630 (10th Cir. 1987), modified on other grounds, 839 F.2d 1383 (10th Cir. 1987), cert. dismissed, 109 S. Ct. 201 (1988). The court further indicated that, even if the application was not an impermissible class claim, Counsel's failure to obtain express authorization to file claims on behalf of the employees, as well as his withdrawal as the class representative, rendered the employee claims invalid. Finally, the court considered employees' request to vacate the prior bar date for their claims based on excusable neglect, but concluded that claimants had failed to prove the standards for mistake or excusable neglect that were articulated in Pioneer Inv. Servs. Co. v. Brunswick Assoc. Ltd. Partnership, 113 S. Ct. 1489 (1993).