Hi Roberto,
What I suggested by changing the Database info to ODBC and OLE DB and then back to the original by using Set Database location in CR Designer was to try to fix the RPT file.
It errors in the SDK because the SDK loads all of the properties into memory on .Load(), if there is a problem the engine will not open the report. CR Designer can work around or ignore some property, because if it is not used then CRD ignores it.
Possibly what may have happened is the rpt file itself may have been corrupted when saving to disk and the SDK has no way to fix it.
If changing datasources in CR Designer doesn't fix the problem the only way to fix the report is to create a new one.
Don