I have resovled this problem just only adding a comment for the stanza and attributes inside the config file inputs.conf.spec as showing below:
FILE => .../Splunk_TA_f5-bigip/README/inputs.conf.spec
Then restart splunk.
I work with Stan here and I was able to fix this by doing the following:
After I pushed these changes to the IDX cluster, we stopped receiving the error message.
That error might because of wrong installation or configuration.
Check below link for hardware and software requirements.
Hope this helps .