You probably don't have the right IOS feature set. Please refer to the IOS Feature Navigator to find out which feature is required on the 2811 to run DLSW.
http://tools.cisco.com/ITDIT/CFN/jsp/index.jsp
Hope this helps,
Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
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Cuauhtémoc, Juárez
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México