[R] Data source name not found, and no default driver specified

[Omar Lakkis]

Using R 2.1.0, RODBC works very well for me. When I move my
application to run for the www-data user under apache I get the
message:

[unixODBC][Driver Manager]Data source name not found, and no default
driver specified

I made sure that the .odbc.ini file is in www-data home's directory
and it is readable. I also defined its location using the environment
variable ODBCINI and verified its value from within R using
Sys.getenv().

I connect using odbcConnect("mydsn") where "mydsn" is defined in the
.ini file. I also tried
odbcDriverConnect("DRIVER=/opt/informix/lib/cli/libifcli.so;UID=myid;PWD=mypwd;DATABASE=dbname;HOST=myhost;SERVER=myserver;SERVICE=service_port;PROTOCOL=soctcp;")
but kept getting teh same error. 

What are the usual suspects in this case? how can I track the source
of this problem?