Everybody is having the same problem with EU roaming data on a Guido membership even though it should just work.
You'll have to contact 48 support and see if they can help at all.
One person claimed that changing their APN settings so that the APN field was set back to 48months.liffeytelecom.com got it working for them.
You may need to switch off and on again after making that change.
Maybe try it and see if it makes any difference.
Can you also post what your APN settings are if you get a chance please?
Thanks.
Hope this helps.