Why my pattern can not be found during run but can be found in offline

Hi,

I am new to Sikuli. I am running the latest Sikuli on Win7x64. Here is my code to detect the top of this page:

find(Pattern("SikuliCodeOx-1.png").similar(0.51))

My run gets the following exception:

[error] An error occurs at line 1
[error] Error message: Traceback (most recent call last):
 File "C:\Users\cwang359\AppData\Local\Temp\sikuli-tmp810604795753824909.py", line 1, in
 find(Pattern("SikuliCodeOx-1.png").similar(0.80))
 Line 9, in file C:\Users\cwang359\AppData\Local\Temp\sikuli-tmp810604795753824909.py

 at org.sikuli.script.Region.handleFindFailed(Region.java:420)
at org.sikuli.script.Region.wait(Region.java:511)
at org.python.proxies.sikuli.Region$Region$0.super__wait(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)

org.sikuli.script.FindFailed: FindFailed: can not find Pattern("SikuliCodeOx-1.png").similar(0.8) on the screen.
 Line 9, in file C:\Users\cwang359\AppData\Local\Temp\sikuli-tmp810604795753824909.py

If I click on the image and choose the Matching Preview tab, it can be found with similarity setting up to 0.95.

Why my pattern can not be found during run but can be found in offline--even after I lower the similarity level from 0.7 to 0.5?