Depending on the error that could just be a permission setting in the ubb control panel.
Who can upload,file type allowed, File size allowed,ETC.
If the settings were always there.
I recall a few users just had to open the options and resave the settings.
If it is a file size issue your new host may have a lower file size limit. You can check that in the control panel>>phpinfo


Blue Man Group
There is no such thing as stupid questions. Just stupid answers