Im not sure why, but at first my things were all working, and i was able to use my inventory on other things when testing my game, but now it says "I can't see that here."

Is there a limit on the amount of items you can use or somthing? if so, how do i make it so i can use more?

It also seems like i can pick up any item i want, but it wont interact with the object it is supposed to interact with...

I.E. at one point you use a key card on a door, and i have the code set to open it... (i know it works, it was working earlier)

but now when i go "Use key on door" it says "I can't see that here."

There is no limit on using items that I am aware of. Is it possible that any of the script got erased during editing, I have had that happen before and did not catch it till I ran a check on all script. There is no need to make "use on" or "give to' commands for objects unless you want them to move somewhere like into another object or give to another person. If you want an object to perform a simple task all you have to do is set up the verb in that objects window and write a script. Set up "use" as a verb for "key" then write a conditional script that says IF player has "key" or IF "key" is available for interaction THEN unlock door (the player types "use key" and the task "unlock door" is performed). You may want to set "flags" to insure better control of the action and appropriate response, EX - set flag "door open" to on when player uses "key" and off when player types "close door" (flags are very useful in conditional scripts). Since the "key and the "door" do not physically have to interact with each other this will work every time, it also allows you to set up an ELSE script that gives a custom response if the condition is not met ("cant see that here" is the prorams generic response when it can not verify an action for an oject within a given room). I don't know exactly how you have it written but I hope this helps.

If you're still having problems just upload the asl file here and someone will take a look at it for you. There is a tab to upload attachments just below the preview/submit buttons on the reply page.

There is no limit on items you can use that I know of.
Sometimes to you may accidently change something and forgot to change it back.