created an attachment (id=157754)
screenshot

description:
exception is thrown out when use report library with name ".rptlibrary" twice.

build number:
2.5.2.v20100201-0630

steps to reproduce:
1. new a library with name " .rptlibrary".
2. new a report design, in outline view, select libraries node and click use
library.
3. select " .rptlibrary" in "use library" dialogue and click ok.
4. select " .rptlibrary" in "use library" dialogue and click ok.
5. use library dialogue pops up: do you want to use this library in the report design, input abc and click ok.

expected result:
no exception.

actual result:
exception is thrown out.

error log:
n/a
fixed. now library namespace can not be empty string or contain some illegal characters.
error message "the namespace " " of the library is invalid, for it is empty or contains illegal characters." pops up.

verified in build (2.6.0.v20100409-0630).