I have 20 3560-48PS Switches that I cannot upgrade the IOS on I have tried using multiple TFTP Servers and XModem transfers but no luck, the switch starts to transfer the file but after about 70% it fails with "%Error opening tftp://172.16.100.203/c3560-advipservicesk9-mz.122-44.SE1.bin"
Any help would be greatly appreciated in this matter.
It sounds like the flash memory on your switch is not big enough of storing two IOS images on it. You will need to remove the current IOS before copying the new IOS. Here is the command to remove the existing image.
delete /force /recurssive flash:/c3560-ipbase-mz.122-35.SE5.bin