Has anyone else had issues using an LT1761 regulator?
If there are RF sources nearby, shielding will help.  However, filtering is generally less expensive.

The most critical place for filtering is the output, as regulation failures are often caused by RF falsing the sense circuit.  However, the input should be protected as well.  Keep the components as small as possible and as close as possible to the pins they're protecting (any distance creates inductance, whether it's on the protected pin or the ground pin).

A pi filter with a ferrite and two caps is a good start.  Choose the ferrite and caps based on the band(s) that EMI is expected to be encountered.  Different values of caps can be used to address different bands, but if they are in parallel antiresonances can occur; having ferrites in between decouples them enough to avoid this.

Simsurfing is a good tool for capacitor selection.  Other manufacturers' caps of the same value and size will behave similarly.  http://ds.murata.co.jp/simsurfing/index.html?lcid=en-us