add instructions to remove old rstudio session

rstudio1.md

@@ -125,10 +125,19 @@ your session via *ssh*:
 ```bash
 ssh ab12cdef@rstudio1.idiv.de 'kill-my-rstudio-session'
 ```
-
 If you can not access the machine via ssh please [ask the
 GSU](mailto:it-support@idiv.de?subject=kill%20my%20rstudio%20session) to kill
-your session.
+your session. Do not forget to include your username.
+
+If you have problems to resume a old session and get the message `Error occurred during transmission` you might need to remove the old session data, which is located in the `~/.rstudio` folder. Usually it is sufficient to remove the sessions folder. The command via `ssh`:
+
+```bash
+ssh ab12cdef@rstudio1.idiv.de 'rm -r ~/.rstudio/sessions/`
+```
+
+If you can not access the machine via ssh please [ask the
+GSU](mailto:it-support@idiv.de?subject=remove%20my%20old%20rstudio%20session) to remove
+your old session. Do not forget to include your username.
 
 
 ### compression