If this particular lens has worked well in the past, on this particular camera, and your camera works fine with another Tamron lens, then I would suspect the lens. If this particular Tamron is not labelled as Di II, it is not meant for cropped-frame Canons such as yours, but for full-frame Canons. See the Tamron web site for full details. The non-Di-II Tamrons will mechanically fit just fine on EF-S bodies, but may not properly communicate with the camera's electronics, causing an error message. One would think that a mis-fitted lens that worked in the first place would continue to do so, but perhaps not.
Canon 7D/5D/40D/1D2N; Nikon F6, D700, FM3A, & Coolpix A; Canon 40mm 2.8 STM, 135L, 50L, 35L, 50mm 1.8 I, 100mm 2.8L Macro, 10-22mm EF-S, 28-135 EF, 400mm 5.6L; Nikkor 50mm 1.2 AI-S, 50mm 1.4G, 50mm 1.8D, 16mm 2.8D Fisheye, 180mm 2.8D, 100-300mm 5.6 AI-S, 18mm 2.8D, Voigtlander 90mm f/3.5 SL II