On the controller which is the source of the captive portal files:
backup flash <enter>
From the UI, select the Maintenance tab, and "backup flash" on the left.
Download this to your workstation and take a look through the resulting files,
the captive portal files are stored under a subdirectory with the name of the captive portal profile:
-rw-r--r-- root/nogroup 3065 2012-06-07 11:58 flash/upload/custom/ACME-cp_prof/acceptableusepolicy.html
-rw-r--r-- root/nogroup 312 2012-06-07 11:58 flash/upload/custom/ACME-cp_prof/cpformat.txt
-rw-r--r-- root/nogroup 10352 2012-06-07 11:54 flash/upload/custom/ACME-cp_prof/acme_planet_bg.jpeg
-rw-r--r-- root/nogroup 8696 2012-06-07 11:43 flash/upload/custom/ACME-cp_prof/Pruebas_Portal.html.org
-rw-r--r-- root/nogroup 8558 2012-06-07 11:59 flash/upload/custom/ACME-cp_prof/Pruebas_Portal.html
-rw-r--r-- root/nogroup 1768 2012-06-07 11:41 flash/upload/custom/ACME-cp_prof/styles.css
-rw-r--r-- root/nogroup 10352 2012-06-07 11:58 flash/upload/custom/ACME-cp_prof/acme_planet.jpeg
-rw-r--r-- root/nogroup 79 2012-06-07 11:58 flash/upload/custom/ACME-cp_prof/logintext.html
-rw-r--r-- root/nogroup 727 2012-06-07 11:41 flash/upload/custom/ACME-cp_prof/usuario_invitado.gif
-rw-r--r-- root/nogroup 8558 2012-06-07 11:48 flash/upload/custom/ACME-cp_prof/acme_step2.html
You must then reconfigure the captive portal by uploading the individual files in the necessary sequence.
Refer to Aruba Networks Support KB 154 and 1293
Best regards