How to go about tracking down this error?

I am using a pico with an ESP8266 for wifi.
I'm writing code that buffers the body of in incoming http request and attempts to write it to a file.

For small files (around 1-2K) it works. As soon as I try with a larger file I get the following error, I think its while I'm still buffering the body of the request.

ERROR: Out of Memory!
at line 1 col 106
...tr(0,c),h[a]=h[a].substr(c)):(b=h[a],h[a]="");return b}retur...
                              ^
in function called from system
ERROR: Error processing Serial data handler - removing it.
WARNING: Unable to create string as not enough memory
WARNING: Unable to create string as not enough memory
Execution Interrupted during event processing.
at line 1 col 189
...+1);h[b[0]]+=a.substr(c+1,f);return"+IPD,"+b[0]+","+(b[1]-f)...
         in function called from system
at line 1 col 106
...tr(0,c),h[a]=h[a].substr(c)):(b=h[a],h[a]="");return b}retur...
                            at line 2 col 73
...E3,function(c){d[a]=void 0})
                              ^
in function called from sysExecution Interrupted

I'm at a bit of a loss of how to go about tracking this down as it looks like its somewhere in the ESP8266WIFI_0v25 or the AT library. I could be wrong, but it doesn't look like any of my code.

Any help would be appreciated.