I want to post the rest of the explanation given to xminus1, so that anyone experiencing this anomaly can be assured it is not an issue that requires servicing. Read on...
On rare occasions, the processor chip on the R2150 may become overwhelmed by the IR input signal resulting in a locked up state. This is evidenced by, as you describe, the 'blue dot' remaining on, while the unit stops responding to commands.
From my experience, this has happened when I have sent, by remote, a series of quick commands.
Although it may happen under other circumstances, it has not been known to be a regular occurrence. As I stated above, it is a rare happening and I doubt you will see this happen again.
Turning off and back on will remedy this. It will not require servicing.