Digital rights firm Perform Group has warned that its 2013 full-year revenue will be below previous expectations, pushing earnings 'significantly' below forecasts. The warning, which also revealed results for 2014 are now set to miss expectations, more than halved the value of the company's stock following the release of the announcement late this morning. Energy services firm Wood Group was also very much lower after it said trading remained distinctly mixed with its Western Canada markets 'weak' and its key engineering division being downgraded for 2014 due to deterioration in upstream markets. While the company stressed that results for the 12 months ending December 31st are expected to be in line with expectations, it warned that project delays offshore, together with upstream weakness in Canada, was expected to result in a reduction in Engineering earnings before interest, tax and amortisation in 2014 of around 15% compared to the current year.Imagination Technologies continued to decline one day after the chip maker said that shipment growth from its partners for the second half would be at a "slightly lower rate than previously seen", due to slowing growth in the higher-end smartphone market.Oxford Instruments retreated from yesterday's strong gains; it had risen strongly after Andor Technology recommended its £176m takeover of the AIM-listed camera maker, putting concerns about a rival bid to bed.Meanwhile, Dialight was making decent gains; the stock was yesterday given a 'buy' rating from Kempen & Co., with a 1,190p target price. Similarly, CSR was a strong riser; the group was given a boost yesterday after UBS increased its target price from 530p to 580p, one day after the group announced that it has decided to discontinue development of its camera-on-a-chip (COACH) platform, which has been sustaining losses from weak demand.FTSE 250 - RisersCSR (CSR) 594.50p +8.29%Dialight (DIA) 853.50p +3.83%Bwin.party Digital Entertainment (BPTY) 118.00p +2.97%AL Noor Hospitals Group (ANH) 915.00p +2.23%Xaar (XAR) 1,167.00p +2.01%Go-Ahead Group (GOG) 1,653.00p +1.54%Ocado Group (OCDO) 408.40p +1.52%Kenmare Resources (KMR) 19.27p +1.42%AZ Electronic Materials SA (DI) (AZEM) 387.90p +1.15%Hikma Pharmaceuticals (HIK) 1,189.00p +1.11%FTSE 250 - FallersPerform Group (PER) 181.00p -57.61%Wood Group (John) (WG.) 716.00p -10.16%Imagination Technologies Group (IMG) 174.30p -8.26%African Barrick Gold (ABG) 155.60p -6.27%Oxford Instruments (OXIG) 1,640.00p -4.43%Hochschild Mining (HOC) 121.60p -3.42%Halfords Group (HFD) 449.50p -3.33%Computacenter (CCC) 654.50p -2.97%Man Group (EMG) 80.25p -2.73%Laird (LRD) 253.50p -2.72%NR