This sounds like the RISC OS 4.39 bug related to opening directories with a large number of files.
We can check this fairly easily. The bug only shows up with directories that have more than 250+ items when RISC OS is running with above 170 (ish) MB of RAM. So, put the RAM allocation down to 128Mb by editing the relevent VirtualRPC config file. Now run VirtualRPC and try connecting to the share. If it opens correctly then it's this annoying bug
You will probably find that you can set the RISC OS RAM allocation to 160Mb without the problem showing up. If the fault doesn't happen at 160Mb then try upping the RAM in 4MB steps until you hit the problem. You can then drop the RAM back by 4MB.