This is a quite interesting issue. Perhaps it may help if we start by trying to understand what caused the issue and then we will consider how you might recover from it.
One of the things that Cisco wanted to do as they released version 15.0 was to improve the security of passwords in IOS. So they designed and implemented a new "type 4" password which they intended to replace the previous "type 5" password used for enable secret or for username secret passwords. So in those versions of 15.0 if you configure enable secret or username secret for passwords the IOS would create the new type 4 password.
Then you reacted to some problem and loaded an older version of IOS. 12.2(55) does not understand the type 4 passwords. So as your switch booted on this version of code and it read lines in the startup config that had type 4 passwords it did not understand them and marked them as invalid input. So the result is that your switch does not have an enable secret and perhaps usernames do not have passwords.
I do not know if you will be able to recover without doing password recovery but I have a suggestion which you can try. See if you can login on the console. It may depend on how your switch was configured whether it will let you do that and whether it will let you get to enable mode on the console. The default behavior was to allow the console to get to enable mode without a password. If your configuration includes aaa authentication enable default enable then the console may not work and in that case I believe that your only alternative will be password recovery.
This is actually a pretty cool feature, i didn't even know it existed until I was looking for a solution to advertise a subnet (prefix in BGP talk), only if a certain condition existed. This is exactly what conditional advertisements does
j ai une question j ai achete un routeur cisco 887VA-k9 , je le configuré avec la configuration ci- dessous
si je le lier avec mon pc portable sur l un de ses ports directement ça marche toute est bien ( la connexion internet + m...
Attached policy provides CLI access to the Cisco 4G router over text messaging. Two files are in the attached .tar file:
2. PDF with instructions on how to load and use the .tcl file.