Siemens driver reading issue

I’ve configured a DataType MyUDT to read data in DB401, 402, 403 from a S7-300 (TCP-IP connection). In MyUDT tags the address DB block nr is parametrized: the address of a tag in MyUDT is e.g.:
where SiteNr will be in the range 1 to 3.
The issue I’m experiencing is that DB401,I174 is available and the value is correct, whereas DB402,I174 and DB403,I174 show up with a red cross like that
and the tag diagnostic says Config error.
I’m sure that DB402, DB403 have been downloaded into the PLC: I can read them with Siemens Step7. moreover I built up a connection from Kepware to the PLC and confirmed that data are there and accessible.

Thanks in advance, regards