Originally Posted by modme

Where did the OP say it was flashing?

The shop probably took of the steering coupler to install the headers. They missed the original spline when they put the coupler back on. When the car detects the steering wheel is not straight when going in a straight line, it will turn on the VDC and Slip lights.

Two ways to fix this:

Reconnect the steering coupler to the correct spline.
Get an alignment.

I would recommend going with repositioning the coupler.