MSSQL Server does not like ILIKE

Using Linq.ilike when the target is an MSSQL Server results in an error, because ILIKE is not known to the MSSQL Server.

Indeed, in this case ILIKE will not work in MSSQL Server. One alternative you can use is simply use Lower to compare: 

Linq['a'].Lower.Like('%inlower')

Of course, but using Aurelius means, that I must neither know nor take into account, what the underlying DBS knows or does not know, should I?

Bernd, that is correct. We even took the effort to add compatibility in minor details, like even the division operation.

But that's not the case here, unfortunately, as that is very different in each database. SQL Server uses collations to define if a query should be case sensitive or not, there is no ILIKE function. There are always minor exceptions, sorry...

Why not implement ILIKE als Uppercase() like uppercase() for MSSQL?

That's something that might be possible. We will have to investigate. I can suggest you register a feature request for that.