error message 550 cant upload pictures

this is the log results I get when trying to upload pictures I never had this trouble when SFTP was free
can you explain what I am doing wrong thank you Jane

28] 550 back-025.gif: not a plain file.
[13:44:28] SIZE beautyofexeter1.jpg
[13:44:28] 550 beautyofexeter1.jpg: not a plain file.
[13:44:29] SIZE bidbridge.jpg
[13:44:29] 550 bidbridge.jpg: not a plain file.
[13:44:29] SIZE BIRemove.exe
[13:44:29] 550 BIRemove.exe: not a plain file.
[13:44:30] SIZE blue-veil.gif
[13:44:30] 550 blue-veil.gif: not a plain file.
[13:44:30] SIZE Button.class
[13:44:30] 550 Button.class: not a plain file.
[13:44:30] SIZE Buttonbar.class
[13:44:30] 550 Buttonbar.class: not a plain file.
[13:44:31] SIZE ballet-girl.gif
[13:44:31] 550 ballet-girl.gif: not a plain file.
[13:44:31] SIZE cara-mia.jpg
[13:44:31] 550 cara-mia.jpg: not a plain file.
[13:44:32] SIZE click.gif
[13:44:32] 550 click.gif: not a plain file.
[13:44:32] SIZE cloudpan2.jpg

Post the log from the transfer queue. To get it double click the first file in the transfer queue (bottom window) which is stuck.