I doubt that anyone here could help you. Your best/only choice is to email Valve's support and clear this out, but don't hold your breath, they are not known for being helpful. Good luck.
Perhaps you traded a gift that was revoked?
Try to remember your last trades, and contact those people, meybe someone got the short stick and reported you.
Probably they banned you cause u have been scammed, so they block both of u and investigate, something similar happens to Merciana (u can look for her on steam and ask her, she would know better than me.)
"Steam Support cannot modify trading or Steam Community Marketplace restrictions, regardless of the circumstances under which your account became restricted. "
I quit trading. It was fun while it lasted, but I'm not tolerating this bullshit.
Hey all. I'm an active member of this community with perfect reputation. Today I received a trade ban for two weeks, without any reason provided. I've never scammed anyone, but have been scammed out of over 20 games. If anyone has contacts with Steam Community Staff it would be highly appreciated so I can dig deeper. Thanks!