I copied about 37mb onto my new PNY 256mb flash drive and all of the sudden I can't put any more files onto it. The computer still recognizes it, and I can delete files from it, so it's functioning except that it won't accept any more files. (I tried 1kb files, so I know they're not too big and I made sure they're not read only.) Why can't I put more files on it?

Would you care to say what the result of the attempted copy was?
If at first you don't succeed, you're about average.M2
"Error copying file or folder. Cannot copy [filename]: The directory or file cannot be created."
Try chkdsk on the flash drive. Or right click properties>tools.
If at first you don't succeed, you're about average.M2
If it's using FAT16, there is a limit as to how many files & folders you can put in the root folder - 512 if LFNs aren't used, otherwise, less. If that's the case, remove some files and create subfolders to use instead (no limit on their contents)
I agree; Computing.Net participants need to proofread
Okay. Creating subfolders solved it. I guess I had too many files. Thanks.
Usually you get some sort of file creation error, so it seemed that could be it. Glad it all worked out
I agree; Computing.Net participants need to proofread
