Also, it might be your LRC, not the magery skill level.
It's been a known bug, since LRC began, that sometimes 100% isn't 100%.
If you have 100% LRC EXACTLY and have no regs, there is a rare chance that a spell can fail from lack of LRC. that's why many people who remember that old bug try to make their suits 101% or higher.
It's thought that LRC from loot-generated items (as opposed to imbued or static items like doom artifacts) might be going by their pre-display intensities instead of what's displayed, so that 100% displayed total from 5 items could be as low as 99% (99% of 100% intensity, on 5 items, totalling 495% actual intensity when the displayed value should be 500%). It's NOT supposed to work like that, but you know how many systems are out there that don't work the way the devs think, and never have. It took until 2007-2008 to convince the devs to recheck the code for Smith BODs with extreme scrutiny, where they found that the LBOD issues people had been complaining about since that system went live were the result of a missing ")" in one line of code - that no one looking previously had noticed.