Trouble updating Cisco ASA 5505 firewall

I'm having issues updating a Cisco ASA 5505 firewall version (8.2) to software version (8.4). I keep getting the error message "error reading/unspecified error". How can I fix this? I'm also using SolarWinds TFTP server to update the firewall.

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ASAFW(config)# copy tftp flash

Address or name of remote host [192.168.0.25]?

Source filename [asdm-641.bin]? asa841-k8.bin

Destination filename [asa841-k8.bin]?

Accessing tftp://192.168.0.25/asa841-k8.bin...

WARNING: TFTP download incomplete!

%Error reading tftp://192.168.0.25/asa841-k8.bin (Unspecified Error)