IIS site not connecting to Oracle database - oracle

Question

I have a server with IIS that hosts web sites.
Some of those web sites (Silverlight) must connect to an Oracle Database to perform queries via OleDb, but they cannot.
Here are the results of what I tested :
'msdaora' provider is not registered on local machine when I run it in the web site
ORA-01019: unable to allocate memory in the user side (when I try to connect with a test console program without administrator status)
Connection OK (with the same test console program WITH administrator status)
ORA-12154: TNS:could not resolve the connect identifier specified when trying to switch to another method of connection (from OleDb to Oracle.ManagedDataAccess.Client)
I went through countless info about these kind of errors but I couldn't find any working solution.
Here is what I tested :
giving "create global objects" right to the relevant users (no change at all)
installing several Oracle clients one after another. Best result is with 10.2 client 64b (where my test program can connect while having administrator rights). The install is clean (no several Oracle folders nor several Oracle environment variables at the same time)
disabling warnings concerning the administrator elevation (ie no confirmation pop up during elevation) : no change at all
checking RAM usage (plenty of memory under the foot)
Additional infos :
The connection string is
Provider=msdaora;Data Source=HOSTNAME;User Id=USER;Password=PASSWORD
Same connection string used with OleDb and Oracle.ManagedDataAccess.Client.
The tsnames.ora file exists (and works, as show my succesful attempt with the administrator test program)
It's working on an older web server, but there are too much differences for me to find any meaningful one (different Windows, 32/64b, different IIS versions, different Oracle client)
Any idea ?

Answer 1

There are several points:
Microsoft msdaora provider for OLE DB is deprecated for ages. You should prefer the Oracle Provider OraOLEDB.Oracle.
Oracle Client and OLE DB provider and IIS application have to have the same architecture, i.e. all must be either 32 bit or 64 bit, you cannot mix them. (ancient msdaora is not available for 64 bit). However, ODP.NET Managed Driver (Oracle.ManagedDataAccess) works for both 32 bit and 64 bit.
When you use ODP.NET Managed Driver then Provider=MSDAORA is not needed in ConnectionString. I assume such attributes is ignored or you just missed to mention it.
Version of Oracle Client and OLE DB provider must match (even minor version). Due to COM limitation you cannot install more than one OLE DB provider for 32 bit and 64 bit each.
Search pattern for tnsnames.ora file in OLE DB is different to search pattern in ODP.NET Managed Driver. Verify following items:
OLE DB reads your Registry for TNS_ADMIN value, the ODP.NET Managed Driver does not.
ODP.NET Managed Driver uses your .NET config file (i.e. web.config, machine.config) to determine location of tnsnames.ora file, the OLE DB does not.
According documentation ODP.NET Managed Driver does take into account the TNS_ADMIN Environment variable and folder %ORACLE_HOME%\network\admin. However, according to my tests it does anyway.
Regarding connection failure is depending on "Rus as Administrator" check permissions of your Oracle installation folder.