Error 451?

An established connection was aborted by the software in your host machine.
451 Transfer aborted. Insufficient memory or file locked.
I get this error message when trying to upload *.jpg files - the memory shouldn't be a problem, so what does 'file locked' mean
I'm using WinXP Home edition if that has any bearing on this.

TIA

also get this -
150 Opening BINARY mode data connection for openG01.jpg
A non-blocking socket operation could not be completed immediately.
451 Transfer aborted. Insufficient memory or file locked.

It is due to long path file or may be its long name,use a small tool available at www.deletelongfile.com which will resolve and unlock it and render it shareable on network,i am sure it will work

It's a problem on the server side. Please contact the server administrator (or web hosting provider) for assistance.