After uploading a new file via Splunk Web, why am I getting "Error: Can't preview source"?

[splunkCiti]

Not able to search newly added file.

I am adding new file from:
setting ->Data Inputes -> New

But after uploading any new file, when I press Next, In Set Source type, there is an error reported "Can't preview the source file" and Data is also not getting indexed.
Because of this, I'm not able to perform any search.
However, I was able to add the file and perform a search before, but suddenly what setting is changed i dnt knw.

[jmallorquin]

Is the file bigger than 500 mb ?
The preview is limited to 500mb

[splunkCiti]

getting this error when i am adding small file also. And file is not indexed also.

[splunkCiti]

Even not getting real time data from forwarder also. When i am performing search on logs of forwarder then data till 9/12/15 is displayed .