Oracle: SQLState=IM004 Driver's SQLAllocHandle on SQL_HANDLE_ENV failed

If coincident you got the above error, what I did was to perform the below;

If you navigate Oracle home you will find that the directory has different permissions then the root of the tree. In the case of 10G the path is C:Oracleproduct10.1.0Client_1. Open the properties for the Client_X directory, and you will see that "Authenticated Users" should have Read and Execute, List Folder Contents, and Read. To fix the problem, do the following....
-Select Authenticated Users
-Uncheck Read and Execute
-Press Apply
-Check Read and Execute
-Press Apply

Edited: Another possible solution toward the above error;
Move ORACLEHOME/bin infront of DEVSUITE/bin entry in the PATH variable

Drop or Remove oracle schema(database)

In order to remove the existent schema in oracle, execute the sqlplus and execute the below command;

drop user user_database cascade;

The once the above command gets executed, the database created by user_database will be removed.

Should you have better suggestion, kindly leave a comment..


;)

Clean uninstall Oracle database

Execute the Universal installer located at:

Start > Programs > Oracle Installation Products > Universal Installer

1. On the first screen click on "Deinstall Products..."
2. Expand the tree view (just so that the second level is visible) and make sure you 3. select everything that is selectable.
4. Click on "Remove..."
5. On the confirmation screen click "Yes"
6. When it has finished click "Close" and then "Exit" to quit the installer
7. Whilst the Oracle installer removes many components there are a number of things that it leaves behind. In order to completely remove all traces of Oracle the following additional steps will need to be taken:

Stop any Oracle services that have been left running. (Start > Settings > Control Panel > Services.)

Services which I have found left behind are 'OracleOraHome90TNSListener' and 'OracleServiceORACLE'. However there may be others depending on your installation. Look for any services with names starting with 'Oracle'.

Run regedit (Start > Run > Enter "regedit", click "Ok"), find and delete the following keys:

HKEY_LOCAL_MACHINE
\SOFTWARE
\ORACLE

HKEY_LOCAL_MACHINE
\SYSTEM
\CurrentControlSet
\Services
\EventLog
\Application
\Oracle.oracle

Note: I have had it reported that some people also have registry entries saved under HKEY_CURRENT_USER\SOFTWARE\ORACLE, this registry entry may be created by some Oracle utilities. If it exists then delete it.
Delete the Oracle home directory:
"C:\Oracle"
This will also remove your database files (unless you located them elsewhere, in which case you will need to delete them separately).
Delete the Oracle program Files directory:
"C:\Program Files\Oracle"
Delete the Oracle programs profile directory:
"C:\Documents and Settings\All Users\Start Menu\Programs\Oracle - OraHome90"
if you did not first run the Oracle installer to remove Oracle then there may be other Oracle profile group directories to remove.
Some of the Oracle services may be left behind by the uninstall. Open ‘services’ on the control panel, make a note of which Oracle services remain and see the notes ‘How to remove a service’ to remove them.
If you didn't first run the Oracle Installer to remove Oracle then you may have some references to Oracle left in the path. To remove these: Start > Settings > Control Panel > System > Advanced > Environment Variables, look at both the use and system variable 'PATH' and edit them to remove any references to Oracle.