This error is associated with using a virus scanning plug-in.
Please look in system log to get more details of the error cause.
If there is the error "Unknown return code from content scanner:" then this can be bypassed by setting "disablecontentscanerror = on" in your e2guardianfN.conf files.
This is clearly documented in the 'AV_SCANNERS' section of the example e2guardianf1.conf file.
#disablecontentscanerror = off
#
# Disable content scanning with error (timeout, AV crash, etc)
# If you enable this option you will allow object with an unexpected result
# Content scanning primarily is AV scanning (if enabled) but could include
# other types.
# With "on" you can allow INFECTED objects
# (on|off) default = off. (default and highly recommended)
If there is the error "scanFile/Memory returned error: NNNN" then either investigate why the virus scan engine you are using is returning the the unexpected error code NNNN and fix that, or turn off the virus scanning.
Regards
Philip