Out of MS-DOS file handles.
Either close some files in Visual Basic or other applications, close other applications, or increase the number of available MS-DOS file handles.
To increase the number of file handles
1 Edit your CONFIG.SYS file using Microsoft Windows Notepad or another text editor. The CONFIG.SYS file is usually located in the root directory of your boot drive. If you don't have a CONFIG.SYS file on your system, you must create one that contains the line listed in step 2.
2 Look for the line that reads FILES = x, where x is some number. Increase the number specified by the FILES command; the exact number of handles you enter depends on the particular applications you run and the number of files that are open at any given time. If other applications open multiple files, you may need to specify more file handles.
As you increase the number of file handles, remember that each handle consumes more memory. For additional information, refer to your operating system manual.
3 Exit Microsoft Windows.
4 Reboot your system, and then try the operation again.