Help with capture CIS Vstim stimulus editor

I have built an amplifier circuit on orcad CIS and i want to give it a Vstim AC input so that I can see the output. I chose Vstim/sourcstm, right clicked on it and choose edit pspice stimulus, choose a SIN stimulus, choose amplitude, frequency and offset value, and press apply, then ok. I then press the save icon, but the "update schematic?" pop-up doesn't come up at all. I then proceed to closing the stimulus editor, and trying to edit the pspice stimulus of the same part again. This time I get this error: "Only one instance of the Stimulus editor is allowed to run. Please close the other instance before starting another one." and if i try to run it, i get an error saying that the ac source has no stimulus property. The only way to be able to access the pspice stimulus of the supply is by closing orcad completely and re-opening it. Any ideas why this could be happening? Thank you very much PS: I tried 2 different Vstim, the other being "Vstim/design cache" and the same thing happened