"Break" button or icon stays gray

[YCZ]

I don't know why the "Break" button/icon stays gray whenever I execute a query. Sometimes I just want to kill the query if it runs too long. The funny thing is that my co-worker's IDE works fine.
Please let me know what go wrong here.
Thanks.

My Support Info:

PL/SQL Developer
Version 8.0.0.1480
12.60746 - 5 user license
Windows XP Professional 5.1 Build 2600 (Service Pack 3)

Physical memory : 2,086,984 kB (1,025,316 available)
Paging file : 4,029,244 kB (3,013,100 available)
Virtual memory : 2,097,024 kB (1,776,788 available)

Parameters
C:\Program Files\PLSQL Developer\plsqldev.exe

Preferences
Session mode: Single
OCI Library: C:\DevSuiteHome_1\bin\oci.dll
Use OCI7: False

Preference Files
C:\Program Files\PLSQL Developer\Preferences\Default\Default.ini
C:\Program Files\PLSQL Developer\Preferences\yxzhang\default.ini

Plug-Ins
*Active Query Builder (C:\Program Files\PLSQL Developer\PlugIns\ActiveQueryBuilder.dll)
*Browser Extender version 2.0 by Joachim Rupik (C:\Program Files\PLSQL Developer\PlugIns\be.dll)
*Version Control Interface 1.2 (C:\Program Files\PLSQL Developer\PlugIns\VCS.dll)
(* is Active)

Aliases
ACES
ACTUDEV
ACUTEST
ALIP
ALIT
...

Homes
DevSuiteHome1 (C:\DevSuiteHome_1)
XE (C:\oraclexe\app\oracle\product\10.2.0\server)

DLLs
C:\DevSuiteHome_1\bin\oci.dll

TNS File
C:\DevSuiteHome_1\Network\Admin\tnsnames.ora

Using
Home: DevSuiteHome1
DLL: C:\DevSuiteHome_1\bin\oci.dll
OCI: Version 10.1
Oracle Database 10g Enterprise Edition Release 10.2.0.2.0

Character Sets
Character size: 1 byte(s)
CharSetID: 0
NCharSetID: 1
Unicode Support: False
NLS_LANG: AMERICAN_AMERICA.WE8MSWIN1252
NLS_CHARACTERSET: US7ASCII
NLS_NCHAR_CHARACTERSET: AL16UTF16

 

[Marco Kalter]

This is because you are using Single Session mode. Switch to Dual Session mode (Tools > Preferences > Oracle / Connection) to resolve this.