Stratix IV - Error 176603: cannot place node <name> at <text> because it cannot...

Hello all :)

I'm using Stratix IV (EP4SGX180KF40I3), with Quartus 11.1SP1.

I have two clock input pins: AB34 and AF6.

I would like to choose between them using a CLKCTRL instance in the design (clock MUXing).

I used the ALTCLKCTRL block from the MegaWizard, with the following configuration:

- For Global clock

- 2 clock inputs

- No enable port

- No "Ensure glitch-free switchover"

The SELECT port for the CTRLBLK was implemented with logic (could receive both '0' and '1' values).

When I run Quartus compilation, I receive the following error messages:

Error (176603): Cannot place node CLK_125M_SEC at IOPAD_X119_Y43_N0 because it cannot drive the node HDP:U1|CLK_RESET_GEN:clk_rst|CLK125M_SEL:U3|CLK125M_SEL_altclkctrl_lef:CLK125M_SEL_altclkctrl_lef_component|sd2 placed at CLKSEL_G0

Error (176603): Cannot place node CLK_125M at IOPAD_X0_Y52_N0 because it cannot drive the node HDP:U1|CLK_RESET_GEN:clk_rst|CLK125M_SEL:U3|CLK125M_SEL_altclkctrl_lef:CLK125M_SEL_altclkctrl_lef_component|sd2 placed at CLKSEL_G4

After getting the error message, I tried also to use a constant value for the SELECT ('0'), but I received again the same error.

My questions are:

- In general: Is it possible to drive these two input clock pins through a CLKCTRL block?

- Do I have anything wrong in the ALTCLKCTRL block MegaWizard configuration?

- Do I I have something wrong in the way I use the ALTCLKCTRL block?

Thanks,

Olga