6. STOCKHOLDERS' EQUITY (Details Narrative) - USD ($)	9 Months Ended
	Jan. 31, 2016	Jan. 31, 2015
Stock Incentive Plans [Member]
Shares reserved for future issuance	39,587,885
ESPP [Member]
Shares reserved for future issuance	2,090,892
Warrants [Member]
Shares reserved for future issuance	273,280
Common Stock [Member]
Proceeds from issuance of stock	$ 44,131,000
Commissions and other issuance costs	633,000	$ 193,000
Common Stock [Member] | June 2014 AMI Sales Agreement [Member]
Remaining Aggregate Gross Proceeds Available Under Agreement	0
Proceeds from issuance of stock	$ 11,456,000
Shares issued, new	8,629,738
Commissions and other issuance costs	$ 311,000
Common Stock [Member] | August 2015 AMI Sales Agreement [Member]
Remaining Aggregate Gross Proceeds Available Under Agreement	22,553,000
Proceeds from issuance of stock	$ 7,447,000
Shares issued, new	6,751,651
Commissions and other issuance costs	$ 190,000
Common Stock [Member] | Equity Distribution Agreement [Member]
Remaining Aggregate Gross Proceeds Available Under Agreement	14,772,000
Proceeds from issuance of stock	$ 5,228,000
Shares issued, new	4,455,278
Commissions and other issuance costs	$ 131,000
Common Stock [Member] | Common Stock Purchase Agreement [Member]
Proceeds from issuance of stock	$ 20,000,000
Shares issued, new	18,518,518
Commissions and other issuance costs	$ 1,000
Series E Preferred Stock [Member]
Shares reserved for future issuance	45,745,760
If converted, Series E Preferred stock holders would receive shares of common stock. Common shares to be issued	13,145,333
Each outstanding share that could be converted into common shares	29
Commissions and other issuance costs		$ 553,000
Series E Preferred Stock [Member] | June 2014 Series E AMI Sales Agreement [Member]
Remaining Aggregate Gross Proceeds Available Under Agreement	$ 10,735,000
Gross proceeds from issuance of preferred stock	$ 60,000
Shares issued, new	2,676
Commissions and other issuance costs	$ 1,000