There can be several possible causes for this:
A: The printer attached to NetROCKEY4 is powered off.
If a printer or any other peripheral device is attached to the parallel port NetROCKEY4, you should turn the power of that device on. NetROCKEY4 dongles require a voltage of about 2.2 volts, and this power is supplied by the mainboard through the parallel port, so if a peripheral device is attached to the NetROCKEY4 dongle, the dongle may not receive enough power to be activated.
B: NetROCKEY4 does not support the parallel mode.
The diversity of computers leads to many different parallel modes, NetROCKEY4 dongles support most modes, but for some special modes it is possible that the system cannot find NetROCKEY4, or NetROCKEY4 dongles do not work well with them. What you need to do is to change the parallel modes, eg. set the port mode in the CMOS setup to ECP or vice versa. If the operating system is Windows NT/2000, you may have to reinstall the driver after you have changed the parallel port modes.
C: The drivers are not properly installed.
NetROCKEY4 requires the installation of drivers, so the settings of drivers may affect the operation of NetROCKEY4. There are 4 options when installing the drivers: “Install NetROCKEY parallel driver”, “Install NetROCKEY USB driver”, “Detect-print-busy mode” and “Not-detect-print-busy mode”, we suggest users to choose “Install NetROCKEY parallel driver”, “Install NetROCKEY USB driver”, and “Detect-print-busy mode”. In Windows NT/2000 only the administrator has the privilege to install drivers.
D: NetROCKEY4 is not compatible with other devices.
The parallel port is not designed to connect many devices at the same time, and in theory only one device can be attached to the parallel port at any one time. With the users in mind, NetROCKEY4 was designed to allow the standard devices, such as printers and scanners, to attach to it, but we cannot guarantee that NetROCKEY4 is compatible with all these devices. Unplug the device to see if it is a compatibility problem.
E: NetROCKEY4 is not compatible with certain PCI-based Parallel Add-on cards
Another issue is that NetROCKEY4 LPT cannot work with certain PCI-based parallel port cards. NetROCKEY4 will treat the card as a sort of hack attack and therefore refuse to communicate with it or the card does not supply enough power to the dongle for it to operate efficiently. If this is the case, we suggest using a USB port NetROCKEY4 instead.
F: There may be a driver or software conflict on the system
Sometimes, the PC drivers may be conflicted or it may be conflict with any of the programs although this is highly rare. Solution: Restart the PC and run the program again. If it still cannot run, try starting up the PC with minimal drivers and programs and check to see if it can run. If it can, this means that it is a software conflict.
G: Driver is busy
This error can occur when the driver or dongle is busy and/or communications between the dongle and PC are interrupted. To rectify this situation, you can add a loop to your program when checking for the dongle. This will ensure that the program will check for the dongle more than once and be able to recognize it properly.