Now its OK.
After Update from 2.4.2. to 2.4.3
Anyhow, thanks for helping.
Now its OK.
I'm having exactly the same problem, however I just did my install yesterday which means I'm using the newest SilverStripe and userforms. No problem with Blog module, or anything else so far (working my way through the silverStripe book)
I "updated" my silverStripe build as described in the update information (meaning I deleted the base folders and did /dev/build/?flush=1)
Tried creating new UserForm pages and to no avail.
I experienced something similar with just a blank page on adding a field. I hadn't RTFM. Renamed the module folder from userforms-0.3.0-whatever to userforms and tada!
Please, it seemed, that with Silverstripe 2.4.3. the story will be ended.
Im sure, that was not only our problem, we test it with all tools which normaly is used by webdesigner, but it was deep inside of silverstripe or the module userdefinedforms.
Thatwhy, please check you version of both and write down,
As I said, I was already using the newest 2.4.3, changing to the "preview" version userforms fixed it for me.
The problem was a migration-problem form 2.4.x to 2.4.y in cominbation with UDF.