As written on
and recited countless times all over the web,
and probably you'd find it on a few pages on MSDN,
the new limit of SQL-Server express is 10 GB, up from 4 GB in the old version.
However, the actual limit is neither 10GB nor 10GiB, it's actually 10'240MB (10 * 1'024 MB).
This is neither 10 GB (10 * 10E9 Bytes) nor is it 10GiB (10'737'418'240 Bytes).
It's only 95% of what I would have interpreted as being 10GiB (10'240'000'000*100/10'737'418'240 Bytes).
This is definitely a bug in the documentation, and may also be considered fraudulent advertising.