Not sure, but those are deprecated variables. The following works:
VERSION=97.0
L_PAYMENTREQUEST_0_NAME0=Socks OC11-002
L_PAYMENTREQUEST_0_AMT0=10
L_PAYMENTREQUEST_0_QTY0=1
L_PAYMENTREQUEST_0_NAME1=Socks TC-001 X2
L_PAYMENTREQUEST_0_AMT1=10
L_PAYMENTREQUEST_0_QTY1=1
L_PAYMENTREQUEST_0_NAME2=Tuxedo
L_PAYMENTREQUEST_0_AMT2=650
L_PAYMENTREQUEST_0_QTY2=1
L_PAYMENTREQUEST_0_NAME3=Paypal Fee
L_PAYMENTREQUEST_0_AMT3=26.13
L_PAYMENTREQUEST_0_QTY3=1
PAYMENTREQUEST_0_TAXAMT=90.50
PAYMENTREQUEST_0_ITEMAMT=696.13
PAYMENTREQUEST_0_AMT=786.63
PAYMENTREQUEST_0_CURRENCYCODE=USD
PAYMENTREQUEST_0_PAYMENTACTION=Sale
As an aside, refer to the PayPal User Agreement section: "4.6 No Surcharges"