Informatica Unable to fetch log

Quite often, you might come across the following error when you try to get the session log for your session.

Unable to Fetch Log.
The Log Service has no record of the requested session or workflow run.

The first place to start debugging this error would be one-level up from the session log, which is the workflow log.
The most common reasons I have seen this happen is because of the following .
a ) One or more of the following parameters have been specified incorrectly.

• Session Log File directory
• Session Log File Name
• Parameter Filename (at the session (and/or) workflow level)

b) You do not have the necessary privileges on the directory to create and modify (log) files.
Whatever be the case , the workflow log is your next point of debugging. In my test scenario , I entered the following parameters for the log file name and directory to simulate this error.
Session Log File directory : $InvalidLogDir\
Session Log File Name : s_m_test_cannot_fetch_log.log
When I ran the workflow, the session failed and I could not get the session log (becuase it was never created) . The error in the workflow log is as follows.

Session task instance [s_m_test_cannot_fetch_log] : 
[CMN_1053 [LM_2006] Unable to create log file
[$InvalidLogDir/download/INFA/QuickHit/ParmFiles/s_m_test_cannot_fetch_log.log.bin].

There seems to be too much guesswork to fix this error based on the posts on internet forums . Somehow, developers seem to think of this error as something wrong with the Informatica client installation.
The next time you get this error, please check your workflow log.
If you have seen this happen before for another reproducible case , please comment and I’ll modify the post to include the same if needed.