According to Haynes.
If the electric roof operates slowly, or the motor appears to be struggling, first ensure that this is not down to lack of maintenance - all the moving parts and slides should be regularly lubricated with light oil (your land rover dealer will be able to advise on a suitable product). The sunroof motor draws quite a heavy current - a battery which is low on charge may struggle to open the roof.
...
The motor incorporates an automatic cut-out facility, which cuts the motor if the sun roof encounters an obstruction - the motor may therefore cur out if the mechanism is partially siezed.
Check all this first as the next step is to take the unit out, and that means taking the head lining down which is no small job.
I hope this helps.