What version and what SP are you using?
Could be several things that cause what you experience:
Most common cause would be, I think : Circular references.
The reason Other peter gave is the most likely.
You have an external reference that is dependent on another reference and the first is dependent on the second one etc..
With update holders you can make your references visible
You can change the order of solving by dragging them into another position. Try to find the right order and maybe your problem can be solved.
But to help you out files are needed. If you can't post them on the forum contact your reseller/var.
With kind regards
Ok, I will look into it. Thanks.
I don't know what to look for. All seems to be fine, no warnings or red, yellow marks.
Even more strange things happens lately. Imported standard parts that I have been used for years suddenly has broken surfaces. Running a repair will ruin all previous mates. I am fixing it by searching copying from old backups where they are still unbroken.
More strange things, which i think is related to the lightweight mode that i started to use for few weeks ago. It seams to screw-up my hole patterns. Holes have changed place whit each other and some sketches have "jumped" to another hole so it is two circles at one hole and some are vithout. All drawings had to be reworked. Have a tank with 16 M10-holes, a sealing and a lid that i did worked back and forth for like 6 month with no problems what so ever. Now when i opens it all the holes are in a mess. Can it be the lightweight that messing things up? Have have been working with SW since Version 1997 Plus and have seen similar behaviors now and then. But i have never trusted the lightweight mode so it is first time im playing with it after reading http://files.solidworks.com/partners/pdfs/WP_PARTNER_BOXX_Maximizing_SolidWorks_Performance_ENG.pdf
Im still puzzled about the need to save aprts again and again and again even though they have never been changed. Even toolbox parts are requested to be saved as soon as open a assembly. Open it again and the same parts asked to be saved again