Receiving the error: "Cannot perform this operation on a closed dataset" while using Database Browser.
Please try the following steps to remove this error:
1] Rename Toad.ini from the Toad folder.
2] Select one of the following options:
a) Select Start | Programs | Oracle | Configuration and Migration Tools | Net Configuration Assistant to regenerate a new tnsnames.ora file.
b) Manually edit the entry in the tnsnames.ora file using a text editor.
c) Replace the existing tnsnames.ora file with a tnsnames.ora file that is working from another computer.
3] Ensure that the tnsnames.ora file is proper with not many spaces between the name and the "=" sign