Solved the problem! The answer came from this post: http://objectmix.com/ado-dao-rdo-rds/392318-fixedwidechar-adodb-problem.html
I had to fix a bug in the ADODB.pas changing the following line
compatible:= FieldDef.DataType in [ftstring,ftwidestring]
into
compatible:= FieldDef.DataType in [ftstring,ftwidestring,ftfixedWideChar]