That setting ("Pause Indexing") means "if there is not 'this much' free space left on disk, stop indexing until there is more free space." This setting is also used for searches. When Splunk runs a search, it needs disk space for saving the search results. The error message says "hey, I don't have enough free disk for saving the search results." The same setting is used for both.
Increasing this number is NOT what you want!
Search results are usually only temporary, but if you have a lot of people saving their search results, they could be using a lot of space.
Or maybe you just don't have enough disk space for your indexes AND your search results.
You can temporarily set the number lower - but you need to find a more permanent resolution to the problem.
Figure out how much indexed data you have on disk and see if you need (1) more disk or (2) to limit the size of the indexers.
Decide if you need to set disk quotas for users to limit the amount of disk they can use for search results. (But be careful, because you want them to still be able to run searches and dashboards!)