php memory limit exceeded when uploading a file (nginx)

previously i had no problem with the file mod.. now i am unable to play media files via veeplay and when i attempt to upload or download files i am seeing 502 bad gateway errors via nginx:

[error] 3289#0: *1411 FastCGI sent in stderr: "PHP message: PHP Fatal error:  Allowed memory size of 50331648 bytes exhausted (tried to allocate 49889280 bytes) in /mysite/mod/file/pages/file/download.php on line 37" while reading response header from upstream, client:, server:, request: "GET /file/download/3148 HTTP/1.1", upstream: "fastcgi://", host: "",

the php memory limit is set to 48M as i don't have much RAM on the server presently.. though i am attempting to upload a 3MB file and the error is still triggered. i disabled 'file_tools' also and that made no difference.

i am running the latest php and elgg versions.
anyone know why this might be? or what i might change?