DNN errors when editing content and changing settings

We have a site originally with DotNetNuke 4.4.1 that was giving a lot of errors, mainly with the FTB html provider but lately it wouldn't let us do changes in the settings, so I upgraded to 4.5.5 following Mitchel Sellers guide. Unfortunately the problems remain - I can only edit text in Basic Text editor and most of the time can't save changes to settings. The site has online shop (CATALook .netstore) which I could only upgrade to match the DotNetNuke version  with Install/Install.aspx?mode=InstallResources" - the Modules Definition page only refreshed when I tried upgrading from there.
The site is in a shared hosting environment - Windows 2003 Server Web Edition SP2 + SQL Server 2005 Express + .Net Framework 2.0.50727.832.
Because this is a site with a shop any promptly response is much appreciated.
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Sam PanwarSr. Server AdministratorCommented:

Your site have full trust permission on the server because DNN 4 + version is not better work without fukk trust permission.

Please also provide exact error message which you are getting so I will assist you.

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goliveukAuthor Commented:
When the site does not accept changes, doesn't log errors as well. The text/html module only works as basic text editor.
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