Custom DataProcessing for ReportingServices

Hi to all, i hope someone can help me.
I'm deploying a new custom DataProcessing Extension (that should work
with webservices but this is not the problem) and before start to
develop mine, i've configured RS to work with
FsiDataExtension(installed as Sample with RS),
BusinessObjectDataSource(from Code Architects Srl that work well with
meb service).
Now i'm going to develop my solution.
1.I've copy and paste FsiDataExtension *.cs files, renamed it with my
name, copyed .dll file in the right RS bin folders, added all xml
portion config to all .config files that need to be modified.
2.I've created new report project, and i've created 3 shared
datasource:
Fsi, Bo and My.
3.I'm going to create a new report:
a.Add New Report
b.Select Fsi DataSource then click -> Next (all work well)
c.Select My DataSource then click -> Next
Shit !! Shit !!!! Shit !!!!
"A connection cannot be made to the database. Set and check the
connection string" Error.
I've add a trace in all constructor of all DataExtension and using
SysInternals.dbgvnt i can see tracing of all DataExtension exception
mine...
what i'm doing wrong '?
Is it a config problem'
Why i'm able to configure all third part DataExtension and not mine '
Should i do something of particular '
tks Simoneok, i'm stupid ! there was an error in .config files :( sorry
if u're having problem with a report in design mode, deploy it and look
in C:\Program Files\Microsoft SQL Server\MSSQL\Reporting
Services\LogFiles folder, i founded the solution to my problem in this
way.